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FLUSHING MEADOWS, N.Y. — There comes a time in every tennis player’s career when they have to do something that truly scares them, something that cuts against how they have played the sport for a very long time. They’ve exhausted all the minor tweaks and cosmetic fixes. Now they have to do the hard reset.
Jannik Sinner had to give up on playing like a human backboard and lean into crushing the ball. Iga Świątek had to stop trying to crush every ball and lean back into the patience that first took her to the top.
Making adjustments like those in the middle of a Hall-of-Fame career is no small thing. They can involve fundamental changes in how a player holds the racket, swings the racket, or makes contact with a ball on any number of shots.
For years now, Coco Gauff has been dancing around a hard reset of the most important and most complex shot of them all.
Ever since she broke out at 15 with her run to the fourth round of Wimbledon, Gauff has had a feast-or-famine serve. When it’s on, it’s a nearly 130 mph weapon that explodes the ball off her racket. It sails past her opponent before she can move for it. When it’s off, the 21-year-old American can give away a set’s worth of points with double faults.
It’s been off a lot lately. Gauff is 4-4 since she won the French Open in June, including a first-round exit at Wimbledon. She has hit 311 double faults in 2025, the most on the WTA Tour and 96 more than the next player back.
After several resolutions not to lose matches to her own serve as much as her opponent, Gauff has stopped the tweaks and gradual adjustments. She is performing reconstructive surgery on a service motion that has been with her since the beginning. And she is doing it at the U.S. Open, her most important tournament of the year and the site of her greatest triumph.
“I needed to make a change, technical change to it, and I don’t want to waste time continuing doing the wrong things,” Gauff said in her pre-tournament news conference.
During her first match at this year’s tournament, against world No. 79 Ajla Tomljanović, Gauff focused on form over firepower. She put first serves in with margin at under 100mph; she tossed the ball more accurately on her second serve, avoiding the drift to her right that makes her body collapse and sends the ball into the net.
But it was the foundations of Gauff’s game — the athleticism, the ball retrieval, and the ability to produce quality on the run — that propelled her to a 6-4, 6-7(2), 7-5 win over the Australian, who was uncowed by the 24,000-strong Arthur Ashe stadium faithful and came close to producing the upset.
Gauff tried tweaking her grip under the guidance of Matt Daly during the past year, but the fundamental flaws in the serve remained. It’s a credit to her other skills that she was able to win another Grand Slam as well as the Tour Finals and climb to No. 2 (now No. 3) in the rankings in that time.
But Gauff did not want to succeed like that. She did not want to leave her results up to whether or not she happened into a good-enough serving week. It felt like a waste of time. And when the time to stop wasting time on an elite player’s serve arrives, the person to call is Gavin MacMillan.
Coco Gauff’s serve troubles have caused her deep frustration the past few weeks. (Dylan Buell / Getty Images)
MacMillan, 59, is a biomechanics expert who does not dabble in psychological explanations for double faults. Players don’t double-fault because they are under stress, he says. They double-fault because their service motion is not as efficient or as repeatable as it needs to be for them to execute it under pressure.
That’s where Aryna Sabalenka was three years ago when she gave in to her mindset and fitness coach, Jason Stacy, and brought MacMillan in to revamp her service motion. Within weeks, she had gone from one of the sport’s punch lines to the U.S. Open semifinals, her double faults dropping into the single digits per match.
“I was really desperate for changes, and I was ready to change whatever, to change my serve and to get better and to finally get back on track with my serve,” Sabalenka said of her work with MacMillan, which continued on and off the past couple of years.
But then Gauff learned that MacMillian, a Canadian educated in America and based in South Africa, was available. And then her team was on the phone with him. And then they were practicing serves in the rain at the Billie Jean King National Tennis Center last week.
“It was, like, a very sudden decision,” Gauff said.
There is no guarantee that Gauff will achieve the same success that Sabalenka did. But Sabalenka said she thinks her improvement happened so quickly because she’d hit rock bottom. That made her willing to do anything and everything that MacMillan told her.
He told her that she was tossing the ball completely wrong, her knuckles facing the sky instead of her palm. He told her that she was pointing her racket in the wrong direction, her strings facing the ground and the back fence. The die was cast before she made contact because her left hand was in the wrong position after she released the ball. That prevented her scapula (shoulder blade) from releasing, pulling Sabalenka down instead of helping her rise to meet the ball.
Sabalenka listened to what he told her. Now she is world No. 1 and defending U.S. Open champion.
MacMillan didn’t set out to be a service wonk. He set out to be a pro. He attended San Jose State University, where he played tennis. Like a lot of people who play tennis, he struggled with his serve. Since the 1990s, he has coached in various disciplines — weightlifting, combat, rugby — but he kept coming back to the serve. He spent countless hours studying the motion of the master, Pete Sampras, the ultimate in that lethal combination of consistency, power and placement.
His light bulb moment occurred when he read “The Spinal Engine” by Serge Gracovetsky, a Russian-born engineer and physicist who theorized that the spine can be the primary driver of movement, power, and locomotion if people can figure out how to use it properly.
“Humans are really limited by joint angles,” MacMillan said in an interview last year. “We usually have to align them and it’s often at 90 degrees.”
He argues that serving a tennis ball involves using the shoulder the same way quarterbacks throw a football and pitchers throw a baseball, but on a different plane. Like them, tennis players need to create a right angle from their elbow to their armpit and down the side of their bodies, while the front side flexes backwards and then snaps forward.
There’s a jump and an arm rotation that come into play as well, but the serve only works if the body gets into that initial position. Even a slight shift, like forgetting to twist the hand that tosses the ball and face the palm toward the sky, can throw it off.
It sounds simple, especially when MacMillan is explaining it, with illustrations of Sampras and Novak Djokovic and their perfect positions. But it can be a lot to take in, especially during a nearly relentless tennis schedule. Gauff will more likely than not need longer than this tournament to figure it out. Sabalenka needed a couple weeks of repetitions before she felt like her new motion belonged to her.
If that sounds impossibly fast to learn a new service motion — golfers can take months, even years, to remake their swings — it’s because it is for mere mortals. People like Sabalenka and Gauff have built their careers on an elite ability to make their bodies move the way they want them to, or in this case, the way a coach is telling them they should move them.
What really matters is that Gauff’s new motion is not for the U.S. Open. It is for the rest of her career. Gauff could have been satisfied with her year. Before winning the title at Roland Garros in Paris, she made the finals of the Madrid and Italian Opens. But that’s not who she is. Winning isn’t winning when she is dumping serves into the net or sending them flying off the court.
“I know where I want to see my game in the future,” she said.
“I’m not going to waste time playing the way I don’t want to play.”
(Top photo: Anthony Behar / Sipa via Imagn Images)