At the start of her first-round match in the U.S. Open, this past Tuesday, Coco Gauff—the winner of the U.S. Open two years ago, the reigning champion of the French Open, and the No. 3 player in the world—tossed up the ball as she began her service motion, and then, thinking better of it, let the ball fall. Ordinarily, no one would note this sort of thing. Tournaments don’t keep stats of caught tosses, which are perfectly legal. But this was not an ordinary situation.

Right before the Open started, Gauff’s home Grand Slam, she had fired her coach Matt Daly, and announced that she was now working with Gavin MacMillan, a serve specialist. The timing of the move, and the decision to reconstruct her serve while also playing her biggest tournament of the year, was unusual, if not unprecedented. Most players on this level don’t tinker much at all with their mechanics, let alone invite millions of people to watch them learn something new. Every toss would rise and fall in the spotlight. On Tuesday, after that first throw, she settled herself, launched the ball up again, and struck an eighty-two-mile-an-hour serve—around forty miles an hour slower than her usual first serves, when they’re flowing.

The point was not to flow—not right now. The point was to think, painstakingly, through every movement: to sense precisely which way her knuckles were turning, to feel the tilt of her scapula, to measure the angle of elbow to her body, to insure that her toss was not drifting rightward (which was one of the reasons, MacMillan had explained, that her body was not extending properly, a failing that had contributed to the spate of double faults that have afflicted her game for years). This kind of overthinking can short-circuit the mind-body connection; athletes train themselves for years to avoid it in high-stakes circumstances.

Gauff is not the first top player to tweak or rebuild her service motion in recent years. Jannik Sinner, Carlos Alcaraz, and Iga Świątek have all tweaked their motions in the past couple of years. Aryna Sabalenka hit double faults at such a high rate that she considered retirement; she turned to MacMillan, overhauled her serve, and then won multiple Grand Slams and ascended to No. 1. But such players tend to make these adjustments in the course of many weeks, on private practice courts in Delray or Monaco or Abu Dhabi, far from TV cameras and prying journalists. Gauff is doing it under the microscope of the press and fans at the U.S. Open.

Gauff has been touted for her potential since she was a child, and has now spent most of her life under intense scrutiny. She has always exhibited a preternatural maturity in spite of it, on and off the court. She defeated Venus Williams at Wimbledon when she was only fifteen, won her first title at fifteen, and, last year, was the highest-paid female athlete in the world. She has grown up in an era when everyone has a camera, and the cameras are often on her. Maybe she imagined revamping her serve while everyone was watching would seem like nothing new.

She could justify the surprising decision. She needed to make a “technical change” to her serve, she said, in a pre-tournament press conference, adding, “I don’t want to waste time continuing doing the wrong things.” She was prepared to lose early, she went on—her focus is on the future, not this one tournament. And perhaps she figured she might lose early anyway, given that she’d been struggling since she won the French Open. After losing in the first round at Wimbledon, she had said, “I just feel a little bit disappointed in how I showed up today.”

Gauff has made changes before, and saw quick, dramatic results. A year ago, she was knocked out of the U.S. Open, as the defending champion, while serving nineteen double faults. She was hitting more double faults than any other player on tour. She had hired Daly then, a grip specialist who had modified the way she held her racquet, and she’d gone on to win her first tournament after they began working together, then the Tour Finals, and the French Open in June. But, despite the shift on her service grip and a new shape to her forehand, her improvement stalled. For years, she had succeeded in spite of her serve, relying on her superior read of the game and her racquet skills and using her speed and athleticism. But winning with grit wore on her, and she imagined how much better she might perform if the glaring weakness of her serve were gone. “I know where I want to see my game in the future,” she said. So there she was, a few days before the start of the tournament, hitting serves in the rain while other top players were competing in the glamorous reboot of mixed doubles for a top prize of a million dollars.

She won her first match, over Ajla Tomljanović, in three dramatic, messy sets, hitting safe, slow serves for much of it, seeming to settle into a rhythm as she went. The two players combined for seventeen double faults and more than a hundred unforced errors. But Gauff held firm at the end, as she so often does, and ripped one of her trademark running backhand passing shots to win it. “This is the match that I needed,” she said in a news conference afterward. “I don’t think it can get any more stressful than this.”

MacMillan’s approach is resolutely technical, not psychological. Serving, for him, is a matter of physics: force and mass, levers and acceleration. He explains that there’s something wrong with the angle of the elbow; he does not say there’s something wrong with the head. If the motion is efficient and sound, he explained to the Athletic before the start of the U.S. Open, it won’t break down. “It’s not a mental thing,” Gauff said, in another press conference, echoing that view. “It’s a biomechanical thing that I had wrong, and I’m just trying my best to get it right.” That could be true. It’s probably easier to fix the angle of the elbow, anyway, than to fix feelings of doubt or anxiety. But the stress that Gauff appears to be experiencing is not ordinary pressure. It seems to have become a kind of exquisite torture.

She caught her first toss in her second match, too, against Donna Vekić. This time, though, she didn’t settle in: she had seven double faults in the first set. After Vekić broke her serve at 4–4, Gauff sat in her chair during the changeover and cried. On the next changeover, as Gauff sat in her chair, her hands were visibly shaking. A trainer came out to examine Vekić’s arm, and Gauff stood up, went onto the court, and practiced her serve while she waited for play to resume.

There is no hiding the serve, no avoiding it, no stepping around it to hit a different shot. Vekić, hampered by an arm injury, was serving as poorly as Gauff, which only heightened the air of desperation in Arthur Ashe Stadium. Somehow, Gauff held on, 7–6, 6–2—a routine scoreline, but hardly a routine win. On the court afterward, she thanked the crowd for the “joy” the fans gave her, then openly wept—tears of relief and even gratitude, it seemed, but not happiness. The match, she told reporters afterward, was “the worst I’ve ever felt on the court,” though she took pride in the way she’d been able to “get up.”

One person in the stadium that night might have understood the position Gauff was in. It wasn’t her coach, who was shouting words of encouragement. The great gymnast Simone Biles was in the stands, and Gauff spotted her. She took inspiration from the thought of Biles on a balance beam, she said on the court, after the match. If Biles could do what she did on the four inches of that beam, she added, then surely she could get a ball into a big tennis court. But Gauff’s mention of Biles brought to mind, for me, the disorientation that Biles experienced at the Tokyo Olympics, when she twisted and lost her bearings in the air—a disconnect between the body and the mind, a condition that can occur under extreme stress. Gymnastics is a matter of physics, too. But there are humans at the heart of it.

At the start of her third-round match, against Magdalena Fręch, Gauff hit her first toss instead of catching it, and this time her serve went in. At last, she wasn’t broken in her opening-service game. Given how emotional she’d been two nights before, how raw she’d seemed, it was hard to expect much from her—except for her fight, which has never deserted her. But, this time, she seemed calmer. Fręch, a steady but not powerful hitter, gave Gauff time to set her feet on her ground strokes. Gauff’s serve steadied throughout the match, too. She cruised, 6–3, 6–1, and finished with a tidy four double faults. Her average first serve was closer to her usual speed. She didn’t seem rushed. It was a remarkable turnaround in a long, ongoing journey. Humans can do extraordinary things. ♦