When Mackenzie McDonald dueled Félix Auger-Aliassime for three and a half hours in the opening round of the U.S. Open, fans were only seeing a glimpse of the time McDonald put in toward his surprise win on Monday.

For both players, and hundreds of others at the sprawling tournament, a match day extends well beyond a warm-up and the contest itself. The preparation, of course, takes weeks and months, with the grueling men’s and women’s professional tennis tours pushing players to seek higher rankings to gain a more favorable path at the Grand Slam tournaments.

And once they arrive in Queens, a new series of obstacles emerges as players adapt to the feel of the courts, the ambience of New York and the demands of one of the world’s biggest sporting events.

For McDonald, the 28-year-old American who broke into the top 50 of the singles rankings in 2022 and upset Rafael Nadal in the second round of this year’s Australian Open, the preparation for the U.S. Open began on Aug. 22 when he arrived in New York. McDonald, who is scheduled to play Borna Gojo of Croatia in the second round on Wednesday, said he trained hard for his first few days, then tapered a bit to recover before his four-set duel against Auger-Aliassime.

Those practices, along with the travel, can become repetitive. Jessica Pegula, the American ranked third in women’s singles, last week compared the routine on tour to “Groundhog Day,” the 1993 film in which a man relives one day again and again. McDonald echoed that sentiment.

“Things can get monotonous week after week, locker room after locker room, hotel after hotel,” McDonald said. “It’s good to have those small goals or little things that drive you that make you believe that you can get better.”

Two Days Out

Two days before his opening match, McDonald couldn’t focus solely on his play. Before practicing on Saturday, he had to stop by a fan event put on by Wilson, his racket sponsor.

His day began at about 8:45 a.m. as he made his way down to the lobby of his hotel in Manhattan’s Murray Hill neighborhood. A driver and S.U.V. were already waiting for him, his girlfriend and his trainer as they walked out of the hotel.

On a normal day, the drive from the east side of Manhattan to Billie Jean King National Tennis Center in Flushing Meadows Corona Park can take up to an hour in heavy traffic.

“It’s never easy,” McDonald said of the commute to Queens. “Day after day, it definitely adds up.”

But on a Saturday morning, with little traffic and an assertive driver familiar with shortcuts, the ride was a brisk 21 minutes 16 seconds.

The quick ride afforded McDonald some extra time to drop off his bags before heading to the Wilson event, where he spent about half an hour volleying with children, then posed for pictures and videos.

With that commitment filled, McDonald could focus on more intense tennis for the rest of his day, starting by working with a physiotherapist and finding time to eat, and following that with two hours of practice.

McDonald’s first hour of practice was scheduled at noon against Marcos Giron, another American player, on Court 4 near Arthur Ashe Stadium. As McDonald and Giron hit back and forth and played out points, dozens of fans stopped by to watch them. As their practice drew to a close, several of those fans began to gather courtside in hopes of an autograph or a picture. But McDonald had no time.

After shaking hands with Giron and his trainer, McDonald quickly grabbed his bags, and scurried off for his next practice on a court on the opposite end of the tennis center, nearly half a mile away.

To avoid having players walk that distance through a sea of fans, the U.S. Open has vans that shuttle them and their trainers out to the farthest practice courts. McDonald and his trainer hopped in a van, but the driver wanted to stay a few more minutes to see if any other players would come.

Already behind schedule, McDonald politely asked the driver if they could leave without waiting. In the early rounds of the tournament, when hundreds of players need to practice, court time is precious.

“They definitely show the glamour of the sport on TV,” McDonald said. “It is all the behind the scenes, it is the day to day and the around-the-year tournaments that we play that really get us to these moments.”

By the time McDonald arrived to his next practice court, it was just after 2 p.m., and the sun was beaming down with temperatures in the 80s. He trained for another hour before finally cooling down and heading back to his hotel to rest.

Last Practice

On Sunday, McDonald wanted to scale back his workload to only an hour of tennis, so he could be fresher for his match the next day. He still did not know his exact playing time, but because it would likely be in the afternoon, McDonald said he hoped to have an afternoon court slot on Sunday.

He was scheduled for 4 p.m. against Lloyd Harris of South Africa on Court 5, where McDonald was scheduled to play the next day.

“Way more of a chiller day for me,” McDonald said, adding that the rest of his Sunday would be spent resting, hydrating and taking “my mind off of tennis for a bit.”

But even when he’s not training, McDonald said there’s other preparation that goes into playing a match, including creating a game plan and looking over analytics.

“The mental preparation for my match on Monday started once that draw came out,” he said.

Match Day

Before McDonald’s match on Monday, there were three others scheduled on Court 5, starting at 11 a.m. Being scheduled later in the day often leaves players trying to figure out how long each of those matches will last so they can plan an ideal time to leave their hotel.

But trying to make those predictions can be a gamble when rain or a lengthy five-set men’s match can delay another match’s start time. At majors, McDonald said that he likes to arrive four hours before a match to be treated by a physiotherapist, hit with a partner for half an hour, have lunch and then prepare his sports drinks and rackets.

“There’s definitely a lot of little nuances that go in part of each day that you’re really submerged in,” he said. “Everything’s invested toward what’s going to prepare me best to play this match today.”

McDonald and Auger-Aliassime finally took Court 5 around 5:45 p.m., and after a quick warm-up, it was 5:51 p.m. when the umpire, Jaume Campistol, said: “Ready? Play.”

From the beginning, it looked like the match was going to be a long duel. It took an hour and nine minutes for McDonald to win the first set on a tiebreaker.

Auger-Aliassime took the second set, but after that McDonald settled in. As McDonald and Auger-Aliassime played on, cheers from Arthur Ashe Stadium overflowed out of the venue, and they could be heard on Court 5. At one point in the fourth set, Auger-Aliassime appeared to complain to the chair umpire about the noise coming from Ashe.

Eventually, after more than three hours on the court, McDonald prevailed, winning the last five points of the fourth set to win, 7-6 (5), 4-6, 6-1, 6-1, and advance to the second round.

Before his win, McDonald said that each incremental victory is what motivates him on tour. The drive to advance, he said, pushes him through long practices, commutes and extensive travel.

“I want to win a title so bad,” said McDonald, who has made one singles final in his career, losing to Jannik Sinner of Italy at the 2021 Citi Open in Washington, D.C. “I always find that each week, your opportunity each week, can be that week that can shift things, and I think that dream is what we’re all chasing.”

And after he beat Auger-Aliassime, the routine of mental and physical preparation began again for Round 2.

Nate Boyer looked up as he began his ascent of Hope Pass about 40 miles into the Leadville Trail 100-mile race. The four-mile section rose 3,200 feet in elevation, taking runners to 12,600 feet above sea level. He would have to conquer the steep grade, run seven miles down the other side to a turnaround and repeat the process. The sun beat down as he maneuvered the trail, devoid of any shade.

“It’s ironic it’s called Hope Pass, because that’s the most hopeless feeling,” Boyer, 42, said after the race. “Like you are pushing the hardest you can to take the next step — and you’re not gaining ground.”

At mile 47, Boyer accidentally jammed his left foot under a rock. His shin swelled, and his leg throbbed. Fifty-three miles to go, he told himself. Keep moving.

Life in football had involved an entirely different kind of pain.

David Vobora, 37, started throwing up when he began the Hope Pass climb. He alternated between walking and jogging as he vomited. A runner in her 50s stopped and rubbed his back as he hunched over again.

At one point, Boyer and Vobora met on the trail. They hugged and offered words of encouragement. The two have been friends for years — and their experience with difficult physical challenges set them apart from most of the other runners.

Vobora was the last pick in the 2008 N.F.L. draft, earning the annual title “Mr. Irrelevant.” He worked his way up to starting linebacker for the Rams and then the Seahawks during a four-year career.

Boyer, a former U.S. Army Green Beret who went on to play football at the University of Texas, was an undrafted free agent who played long snapper in preseason games for Seattle in 2015.

Now, both men were trying to become the first former N.F.L. team members to finish the punishing 100-mile race before the 30-hour cutoff.

“Just being up against that distance, that elevation, that length of time — the mountain will make cowards out of all of us,” Vobora said. “It feels more spiritual than you versus an opponent. It’s you versus who will show up internally.”

After Vobora’s N.F.L. career, he founded the Adaptive Training Foundation in Dallas, which provides free training and community to wounded, ill and injured military veterans and civilians. He became interested in running Leadville after pacing a friend for 18 miles in 2021.

Vobora had started running during the pandemic. He ran 10 miles one day and felt surprisingly fine afterward. In April 2021, he completed a marathon, running loops around a pond, and then tried 100 miles in 24 hours, finishing with nine minutes to spare.

“I was a total mess afterward,” Vobora said. “Laying on the ground. I couldn’t eat. I was peeing blood.”

But he said he had also thought, “How far could I take this?”

To prepare for Leadville, Vobora started an intense training schedule. He stopped drinking alcohol and ate only meat and fruit, dropping from 255 to 205 pounds to adopt a more runner-like build.

“Before Leadville, it was about taking on the task and having the buckle,” he said, referring to the belt buckle runners receive for finishing. “Now it was, ‘You’re going to do this because you said you would.’ The stakes were so high, and it took 100 percent of me to train, maybe for the first time since football. That was something I had missed.”

Boyer is a filmmaker and a co-founder of Merging Vets and Players, a nonprofit organization that helps combat veterans and former professional athletes make transitions to new lives. He also hosts the Discovery Channel show “Survive the Raft,” in which contestants work together on a raft to complete challenges.

In 2022, Boyer ran the Austin Marathon and, five weeks later, a 50K. After the latter race, he said, he didn’t feel the bone and joint soreness he had experienced after the marathon.

“I thought, ‘That’s interesting,’” Boyer said. “‘Maybe I’m more made for this distance?’”

So Leadville it was.

“I don’t know if it’s about running at all,” Boyer said. “It’s the challenge of seeing what your body is capable of. A lot comes from a very deep-seated insecurity, most likely — feeling like you need to do something incredible with your life..”

Gummy Worms and Pretzels

The Leadville 100, which begins and ends in Leadville, Colo., started at 4 a.m. on Aug. 19. Runners traverse the Rockies in what organizers describe as a “true elevation roller coaster.” High-altitude sections, trails and paved roads, and technical sections of the Colorado Trail combine for over 15,000 feet of net elevation gain.

Seven hundred runners ranging in age from 18 to 72 started the race. Only 365 finished within the time limit.

Six and a half hours after the start, Boyer entered Twin Lakes, the aid station at Mile 37.9. His three-person crew laid out gummy worms, bars and gels for energy, pretzels and other snacks. Boyer sat in a folding chair and changed his socks and shoes. He drank coconut water and ate blueberries and a banana.

“My legs are killing me,” Boyer said. “My back hurts. And I’m dehydrated.” He paused and smiled. “Otherwise, life is great.”

A couple of hours later, Vobora jogged into Twin Lakes. His eight-person crew had set up a tent near the aid station entrance.

His tone was all business. “The things that hurt the worst are my knees,” Vobora said, who also said he was cramping.

His wife, Sarah, unpacked and repacked his bag. “Pack the big gloves,” Vobora said. “My hands went fully numb this morning.” Temperatures seesawed from the low 40s at the start to the high 70s midday and back into the 40s that night.

“I feel like I should be further than 38 miles,” Vobora said, chuckling, as he started jogging away. “My energy is good. My stomach has been all over the place. I’m trying to force-feed myself so I can have all the energy for the climb back up Hope Pass the second time. My main thing is the clock. The time stamp getting back over to Twin Lakes before 10 p.m. That’s the cutoff, right?”

What Went Wrong?

Vobora had arrived in Leadville two weeks before the race to acclimate to the elevation. He had a detailed 28-hour race plan: go fast on the downhills, aggressively hike the ascents. Remain steady on the flats. While football is a team sport in which everyone must work together, for Leadville, Vobora would be running alongside people with their own individual goals and motivations. He liked that distinctive challenge.

“Of the hundreds of miles leading up to this race, I’ve probably felt good in about 10 percent,” Vobora said before the race. “Maybe 20 if I’m being liberal. The rest have just been work.”

After almost 17 hours on the course, Vobora trudged back into Twin Lakes. On Hope Pass, he hadn’t stopped vomiting for three hours. He had experienced intense cramping. A medical official had recommended that he drop out, and he relented.

As he rode the shuttle down the mountain, he leaned his head against the window and bawled.

“Damn it, man,” he said, his voice catching. He started talking about his strategy for next time: He would put someone at every aid station. “They’ll have a bag and say, ‘Here,’ and I’ll keep running. I know I can run this thing.”

Vobora walked to the tent where his crew waited. He and his best friend, Mo Brossette, also a member of his support team, tried to determine what had happened: too many salt tablets? Too much food?

“I’m so mad right now, dude — and I’m so sorry, you guys,” Vobora said to his crew.

The next day, Vobora reflected in a text message: “More and more grateful each moment that I did not complete it. Because the questions I am asking and the places I am exploring … I couldn’t be here without it.”

Boyer had arrived in Colorado the day before the race, staying in a hotel 40 minutes away from the starting point. As darkness fell and the temperatures dropped, he tried not to overthink the miles he had left. “Focus on what you can do in these next few steps,” Boyer had said before the race. “The mountain won’t look like it’s getting any closer if you keep looking at it.”

Vobora said the physical challenge of an ultramarathon was entirely different from the pain of playing football, which he said involved “short bursts that are very aggressive, warring, violent actions.”

He continued: “Ultramarathoning is the complete opposite side of the coin. It involves patience. It involves the state of sort of equanimity to approach difficulty and pain.”

Chris Long, an 11-year N.F.L. veteran who now has a foundation dedicated to providing education and clean water around the world, is a friend of both Vobora and Boyer; both have worked with him on foundation projects.

He said their experience in football had prepared them well for the challenge of Leadville.

“Playing in the N.F.L. teaches you how to turn your brain off, put your head down and work,” Long wrote in an email. “You get good at going to your ‘happy place’ and distracting your mind from the challenge itself.”

‘Is There Any Beer?’

After more than 24 hours on the course, Boyer crested the second-to-last hill. Stars were scattered across the sky as he ran, headlamp on, toward the finish line a block south of Leadville’s main street. Small pockets of spectators cheered as he jogged the final ascent.

“Let’s go, Nate — what a finish!” Mitch Moyer, his crew chief, yelled as he ran alongside Boyer.

Boyer finished in 24 hours 31 minutes 7 seconds. The announcer called his name out to the nearly empty stands. Boyer was the 57th male finisher and the 63rd finisher overall. He embraced Merilee Maupin and Ken Chlouber, the race’s co-founders.

“Do you want anything?” Moyer asked.

“Is there any beer?” Boyer asked, smiling. Moyer handed him a nonalcoholic beer. “That’s actually better,” Boyer said. His walk turned to a hobble, and he began to shiver.

Racers who finish in under 25 hours receive a bigger buckle than other finishers get. As Boyer walked to retrieve his, the pain started to set in.

“Is running fun for me?” he said, laughing. “No. It’s not. It’s therapeutic — but therapy is not always fun. There’s nothing better than finishing a run, no matter what the distance. The worst part is starting it, and the best part is finishing it. Everything in between is up and down.”