Conner Mantz’s arms were shaking as he warmed up for the Olympic marathon trials in Orlando in February.

Mr. Mantz, 27, of Provo, Utah, looked over to his close friend, Clayton Young, who was stretching next to him. The two men had run more than 10,000 miles together. They had raced for the same prize money, fought for the same spots on the podium — and formed a bond so strong that other runners said they wished they could replicate it. They had supported each other through season-ending injuries, and pushed each other through grueling training sessions.

Their friendship has lifted both runners to the peak of their professional careers. Both believed they had gotten the other to the starting line that day. Now, they hoped to get each other to the marathon at the Olympic Games in Paris. They had a real shot: Mr. Mantz was a favorite to qualify, and Mr. Young was a strong contender.

If they made the team, their years of grinding out monotonous miles would be rewarded with the opportunity to represent their country, and an even better chance at financial security for their families.

But so much could go wrong in the two-plus hours it would take to complete the race, and Mr. Mantz and Mr. Young had daunting competition, including the four-time Olympian Galen Rupp and a score of other competitors who might surprise them.

By the time the runners approached the starting line, it was 61 degrees with 65 percent humidity — the kind of warm and muggy weather that makes a 26.2-mile race even more of a test. Mr. Young held a bag of ice in his hands in an attempt to stay cool. He and Mr. Mantz, both wearing white hats and black sunglasses, shook their limbs nervously as the countdown began.

About 200 men stood twitching at the starting line. It was likely that only two would get places on the U.S. Olympic team.

The horn blared. The two friends bumped fists and started running.

A Parallel Path to Elite Running

By the time Mr. Mantz and Mr. Young met at Brigham Young University in 2017, both had established themselves as rising stars in distance running.

Mr. Young, now 30, started running in fifth grade thanks to a program called the Mileage Club. Every lap he ran around the soccer field during Friday recess put him closer to earning prizes, like a keychain with a tiny foot. It was also a chance for Mr. Young to race against one of his childhood friends, named Alex. Even then, he loved the competition, and the back-and-forth between friends that motivated them to log more miles.

Mr. Mantz decided at age 12 that he wanted to run a half marathon after watching his older brother and father do the same. When his father started to run marathons, Mr. Mantz announced that he wanted to run the full 26.2 miles, too. (After consulting his doctors, his parents pumped the brakes — but they did let him join the cross-country team.)

Both Mr. Mantz and Mr. Young found joy in the sport. By the time they joined their high school track and cross-country teams, their potential was clear. College coaches soon started calling.

Mr. Young chose B.Y.U. in part because it favored the team over star athletes. Two years later, Mr. Mantz arrived, drawn partly by coach Ed Eyestone, who had run two Olympic marathons himself. The university is supported by the Church of Jesus Christ of Latter-day Saints, of which both runners are members.

Mr. Mantz and Mr. Young said their faith puts their running in perspective: Like all athletes, they have faced injuries and setbacks, and can get sucked into the cutthroat nature of competition, even with each other. But, as Mr. Mantz put it, “we are very focused on the eternal.”

Mr. Eyestone can’t recall the moment when he saw something click between the runners, but their connection quickly became clear. While there is a natural competitiveness among elite runners, Mr. Mantz and Mr. Young were “comfortable enough with one another that the ego does not get in the way of workouts,” Mr. Eyestone said. Mr. Mantz liked to lead the pack and set the pace, and Mr. Young could follow without turning practice into a competition.

That doesn’t mean that race days were as cordial as practice. “He doesn’t want to get beat, and I want to beat him,” Mr. Young said. He is the more analytical of the two: Mr. Young pores over his training data, and closely follows the research on human performance to help the pair improve.

“He’s always trying to find the next best thing — what can we do better?” Mr. Mantz said.

When Mr. Young graduated with a degree in mechanical engineering in 2018, he had a decision to make — sign a professional contract that would require him to move out of state, or stay in Utah, where Mr. Mantz still had two years left in school.

He chose to stay, in part so he and his partner could continue to train together, with the idea that Mr. Mantz might stay after graduation, too. A running contract with the shoe company Asics made it financially possible for Mr. Young.

The two spoke of these choices delicately. “It was his decision he had to reach by himself, and he did,” Mr. Young said. But they shared the same belief: “If we went our separate ways, I just don’t think we’d be as good as we are now,” Mr. Young said.

‘Where’s Clayton?’

There was never a guarantee that the United States would have a men’s marathoner at the Paris Games. To secure even one spot, at least one American man would have to finish a marathon, somewhere, in under 2 hours, 8 minutes and 10 seconds. That was the threshold for having a team at all.

There was a twist, detailed in the 24 dense pages of U.S.A. Track & Field’s athlete selection rules: Achieving that time wouldn’t necessarily secure a place on the team for the person who ran it. It would simply create a spot that someone could then win by performing well at the marathon trials in Orlando.

And no matter how many American runners beat that time, the United States would send no more than three men’s marathoners to Paris — the cap set for each country.

As the 2024 Olympic year approached, Mr. Mantz and Mr. Young focused on running the qualifying time. No one had achieved it by October 2023, when they lined up for the Chicago Marathon. The course is flat and fast, giving the field a better shot at beating the time.

Their wives, Ashley Young and Kylie Mantz, crisscrossed the Chicago course, trying to glimpse their husbands as often as possible along the winding route. They were comforted to see them sticking together. “There’s no better person I’d like to have next to Conner,” Ms. Mantz said of Mr. Young.

As they cheered, they kept one eye anxiously on the time. They share the same nerves on race day: Both women know how hard their husbands have worked, the results they want, how their race times and finishes can affect their livelihoods. They understand how unpredictable and brutal a marathon can be — and on race day, they have little interest in talking to anyone who doesn’t.

During the final stretch of the Chicago race, they were leaning over barricades, necks craned, looking for their husbands flying by at a pace close to 4 minutes and 53 seconds per mile.

When Mr. Mantz passed them at Mile 23, every breath powering him toward the finish, he used his precious energy to shout one thing: “Where’s Clayton?” Mr. Young was close behind him.

When Mr. Mantz finished in 2:07:47, he turned around to see Mr. Young cross the finish line just 13 seconds later. They clocked the fifth and seventh fastest marathon times ever for Americans and were the only Americans who achieved the threshold time for Paris. But they still had to win their places on the team.

‘Just Stay Together’

Over the years, the two runners’ families have become close. As soon as Mr. and Ms. Mantz stepped into the Youngs’ house on a recent afternoon, Ms. Young asked whether they were hungry, opening the fridge to grab fruit and yogurt before they’d had a chance to answer. As Mr. Young and Mr. Mantz went outside to stretch, the Youngs’ daughters, Lucy and Jenna, tagged along. They adore Mr. Mantz, whom they call “diddum.”

But after the Chicago race, like most others, Mr. Mantz and Mr. Young didn’t contact each other for a few days. It went unsaid, as it always did, that they needed time to themselves.

At times, Mr. Young and Mr. Mantz sound less like competitors and more like an old married couple. They know how to compromise. (Mr. Young likes to run later in the morning, while Mr. Mantz is an earlier riser. They meet in the middle, at 7 a.m.) They can press each other’s buttons — like when Mr. Mantz pushes the pace during a workout, at times to Mr. Young’s frustration — but they also know when to lay off.

“We have to dance around each other sometimes and work through our emotions and feelings,” Mr. Young said.

They were soon back together to begin a training cycle for the Orlando trials.

There were still only two guaranteed spots available on the Olympic team — the two they had created in Chicago. Technically, another runner could still unlock a third spot. But if they didn’t, both Mr. Mantz and Mr. Young would have to finish first and second to make the team.

For much of the race, they followed a runner named Zach Panning, letting him do the work of leading and setting the pace. By the time they reached Mile 18, they knew they were in the position to qualify for Paris. The anxiety that had Mr. Mantz’s arms shaking at the start of the race had given way to a loose, controlled show of excitement. Mr. Mantz reached back to high-five Mr. Young.

In the last two miles, though, Mr. Mantz started struggling. He had stumbled at the end of races before, his muscles and lungs pushed to the brink. He feared he wouldn’t finish.

He asked Mr. Young to step ahead of him, to block the headwind that makes the final miles even harder. Mr. Young shifted his position. “Just run behind me,” he told Mr. Mantz. “Just stay together.”

The pair was stride for stride, as they have so often been, as they approached the finish line in first and second place. In the final steps, Mr. Young signaled Mr. Mantz to take the win, even though that meant giving him the extra $15,000 in prize money that came with first place.

They looked awe-struck as they broke the tape, making them the only two American men to qualify for the Paris Olympics.

“When I think of the reason I stuck by Conner in the Olympic trials, it’s because I knew I would be better in Paris with Conner by my side,” Mr. Young said, as Mr. Mantz nodded. “Not just in the Olympics, but in training.”

This time around, they didn’t have much of a break. They were quickly swept up in the excitement of qualifying for the Olympics: a trip to the Utah State Capitol and a string of media appearances and sponsor meetings.

And they already had another race on the calendar: the New York City Half Marathon in March. A few days before that race, Mr. Mantz had to drop out because of an injury. He couldn’t be too careful before the Olympic training cycle began.

That left Mr. Young to train without his partner. As he tied his shoes at home in Provo before a solo run one recent morning, he looked around, as if he were missing something.