Josh Zipin of Manhattan rushed over from Arthur Ashe Stadium to the Grandstand court of the Billie Jean King National Tennis Center on Thursday hoping to catch the final set of John Isner’s singles match. Zipin, 34, said he had never seen Isner play live, and wanted to see what his “insane” serve looked like in person.

“Somebody behind me was asking if Isner served to you 100 times, how many times could you return it in the court and the person sitting behind me said one,” Zipin said. “I think that’s probably being generous.”

For 16 years, Isner, the 38-year-old American star, has wowed fans around the world with his signature game, which combined a booming serve, powerful groundstrokes, and quick hands at the net with volleys and overheads.

A North Carolina native who stands at 6-foot-10, Isner is the career ace leader in the history of the men’s tour. But he is perhaps best known for winning the longest match in tennis history when he played for 11 hours 5 minutes over three days against Nicolas Mahut of France at Wimbledon in 2010. That match led Wimbledon to institute a final-set tiebreaker. (If you have 11 hours to kill, you can watch the match in full here.)

Isner was in the top 20 of the singles rankings for 10 straight years, from 2010 to 2019. He was a U.S. Open quarterfinalist in 2011 and 2018, a Wimbledon semifinalist in 2018 and has earned nearly $23 million in career prize money, but was unable to win a Grand Slam tournament title.

Andy Murray, one of Isner’s contemporaries, said during an interview this week that Isner “was always a disaster to play against or see in your draw,” adding that “his serve’s the best of all time.”

Thursday would turn out to be the last time he would fire that serve at a pro event. Isner had announced on X, formerly known as Twitter, before the U.S. Open that the tournament would be his final act so that he could spend more time with his wife, Madison, and their four children.

“This transition won’t be easy but I’m looking forward to every second of it with my amazing family,” Isner wrote. “Time to lace ‘em up one last time.”

Isner won his first-round match on Tuesday in straight sets against Facundo Diaz Acosta, an unseeded player from Argentina. A number of his cohort, who have since retired, including Bob and Mike Bryan and Sam Querrey, were in attendance.

On Thursday, he was defeated in five sets by a younger American named Michael Mmoh, who stayed composed despite playing before a crowd that was solidly in his opponent’s corner.

When the match was over, Isner buried his head in a white towel and fought back tears. He could barely speak during the on-court interview.

Mmoh said the match was “no doubt the biggest win of my career,” and he congratulated Isner on a remarkable, trailblazing career.

Lisa Katter, 54 of Long Island, said she was impressed by Isner’s performance. “I can’t believe even at this point in his career he’s still acing an entire game,” she said.

Then, not quite ready to call it a career, Isner slung his bag over his shoulder and trudged off to play doubles. A few hours later, that too was in the books, as he and fellow American Jack Sock, who is also retiring after the U.S. Open, lost in three sets.

Later, Isner said that he was feeling many emotions — disappointment over how he played, gratitude to have one last time to compete in the atmosphere at the U.S. Open, and pride in what he achieved throughout his career.

“It just didn’t go my way today,” he said. “It’s a tough way to go out but at the same time I went out in front of a packed stadium and a standing ovation and it was pretty cool.”

He said it was hard to explain how badly his body has felt recently, and he was looking forward to not having to practice anymore. He said he looked forward to finding what he was passionate about, and devoting more energy to being a good husband and father.

“Tennis is a,” he started before trailing off and lowering his head to gather himself. “It’s been a huge part of my life so it’s tough to say goodbye, it’s not easy.”