A huge talking point entering this year’s US Open was Coco Gauff’s enlisting of biomechanist Gavin MacMillan to improve her serve. MacMillan, who did the same with Aryna Sabalenka, was seen working with Gauff on the practice courts in the week leading into the main draw.
Many observers believed this was wildly unconventional. What player, let alone one of Gauff’s stature, would retool a shot this close to a major tournament? Technical changes are extremely difficult to make for pros who have spent years learning and grooving strokes a certain way.
Yet Gauff—who survived Ajla Tomljanovic in a first-round epic on Tuesday night—is not the only top player to have recently remodeled technique on certain shots.
Iga Swiatek
Iga Swiatek emerged at the start of 2024 with a streamlined service motion, smoothing out a hitch previously present in her takeback. The change has paid dividends, coinciding with a significant increase in her average serve speed since 2023. In fact, it’s risen to the point she recorded the fastest average serve speed—approaching 111 mph—among women at Wimbledon in 2025.
The missing piece of the puzzle, current coach Wim Fissette told Bounces, was direction.
“In the past, she didn't believe much in the serve, so she was going a lot with body serves. And now, step-by-step, I convinced her to go more for the spots and go for it,” he explained.
“It's been really good. I saw the stat that she was winning 78% of the first serves during the [2025 Wimbledon] tournament, which was incredible.”
In her first-round win over Emiliana Arango on Tuesday in New York, that number hit 88%.
Jannik Sinner
Following Swiatek into Ashe on Tuesday was defending US Open champion Jannik Sinner, another player who has reworked his serve.
His change involves foot placement; Sinner switched from a platform (feet apart) to a pinpoint (bringing feet together) stance.
As Sinner’s coach Darren Cahill told the "Served with Andy Roddick" podcast in June, he and co-coach Simone Vagnozzi had planned to introduce this switch at the end of 2023, part of a “three-step plan” to improve a delivery which they believed was too side-on and lacked shoulder rotation.
Yet after a shock loss to Daniel Altmaier in the second round of Roland Garros that year, Sinner wanted to make the change immediately. They hit the practice courts the next day, initially emulating John Isner’s motion before Sinner developed his own feeling and action.
“As soon as he went to the step-up serve, we could see that there were improvements to be made and he felt much more comfortable doing it,” Cahill recalled, also revealing Vagnozzi had helped Sinner shorten his backswing for a more effective backhand.
Six months later, Sinner won the first of four Grand Slam titles at the 2024 Australian Open.
Aryna Sabalenka
Fellow US Open defending champion Aryna Sabalenka began making technical changes on her serve back in 2022. That season began in nightmarish fashion in Australia when she was plagued by service yips, and within six months MacMillan was on board.
He set about removing the flaws he spotted in her action. “The reason her ball toss gets [too] high is because … her weight’s back, but her arms haven’t caught up. And she has a pinpoint stance, so she steps up, her arm’s now going back as her body’s going forward. The only way she can catch up to it is if she keeps the ball toss high,” he told Performance-Plus Tennis.
“When she gets really fluid with her takeback, her weight-shift is all together, she keeps the wrist angle at the right [neutral] angle, her toss isn’t high.”
MacMillan helped Sabalenka better sync all of these elements, and within six months her renewed serve helped her triumph at the 2023 Australian Open.
MacMillan also helped Sabalenka make forehand adjustments. "Before I was trying to over-rush things, try to run to the ball, meet it earlier, which actually makes sense, to take time from the opponent,” she told Tennis.com. “I have to actually wait for the shot and the right moment to actually hit the forehand, to make that rotation, which gives me much more power and control on the shot.”
Ben Shelton
American star Ben Shelton also worked on altering groundstroke technique. The powerful-serving lefty was already a Slam semifinalist who reached the brink of the Top 10 in 2024.
But he didn’t want to simply rely on his huge serve. Plus, coach and father Bryan Shelton had noticed a technical flaw in his backhand—his grip made his racquet face too open, denying him topspin and margin.
“It was definitely a fix, something that we looked at in the [2024] off season, the greatest backhands on tour and in history, what that swing path looked like, how they hit it, the speed that they hit it at, how they were able to go both directions with it,” Shelton told atptour.com. “That one technical fix that I made, and I spent a lot of hours on this offseason, started to come together when I played my first match in Auckland, and then by the time I got to Australia, it started feeling really good.”
So good, in fact, that he stormed into the 2025 Australian Open semifinals, then later won his first ATP Masters title in Toronto.
He entered the US Open at a career-high ranking of world No. 6.
Carlos Alcaraz
As Shelton honed his backhand, Carlos Alcaraz continued to refine his serve. The Spaniard scooped back-to-back Slam titles at Roland Garros and Wimbledon in 2024 all while adapting to a new service motion—aimed at removing a pause in his motion—that coach Juan Carlos Ferrero introduced before that year’s clay-court season.
In 2025, there are more visible differences at multiple stages of the service motion, including racquet positioning, knee bend and swing path—all designed to create more power.
At times this year, Alcaraz’s ace count has spiked to new heights. While in his opening win at the 2025 US Open, he won 86% of first-serve points against Reilly Opelka, peaking at a speed of 132 mph.
“It’s a constant task,” Ferrero told atptour.com. “The serve depends on a number of things; practice, feeling relaxed about the new movement, feeling comfortable.”
