Ahead of the US Open, Coco Gauff made a bold decision to shake things up and it definitely turned heads. She brought in biomechanics expert Gavin MacMillan—yes, the same coach who worked wonders with Aryna Sabalenka—specifically to sharpen up her serve after battling ongoing issues with it. And what issues they were. Her first serve betrayed her time and again, leading to nightmarish double fault counts, including a staggering 23 in one match against Danielle Collins at the 2025 National Bank Open. Across this season alone, she racked up 347 double faults! It was a problem she just couldn’t shake. But now? It looks like the tide finally might be turning.

Thursday in Beijing told a different story, as Gauff fended off Germany’s Eva Lys in a fiery quarterfinal clash. The 6-3, 6-4 scoreline looked neat on paper, but the intensity was much higher on court. Gauff, already a two-time Grand Slam champion, marched into the semifinals at the WTA 1000 by striking early and converting three of four break points in the opening set. Afterward, she summed up her approach perfectly. “I’m happy with how I played—she’s a tough opponent and she hit some incredible shots on the run but I tried my best to play aggressive and good tennis,” she said in her post-match interview. And the stats? They backed her up every step of the way.

A look at Coco Gauff’s serve percentage during the match

The American put her stamp on this quarterfinal with an assertive performance across the board. She dominated total points won at 56.1%, pulling ahead of Lys and showing composure in the key moments. On serve, Gauff kept the pressure high. She fired 3 aces and landed a healthy 78.1% of her first serves. The double faults crept in, she tossed in 4, but her numbers held strong. She secured 62% of her first-serve points and won half of her second-serve attempts. That balance kept her service games steady and under control.

Break point conversion was another highlight for Coco. She made the most of her chances, converting 5 of 9 opportunities and breaking Lys whenever the door opened. On defense, she stood tall. Gauff faced seven break points and saved four, keeping her lead intact and the momentum on her side. Her total return points won reached 52.5%, showcasing her relentless style and eagerness to attack on the return. From start to finish, Gauff dictated play. She broke Lys’ serve three times in the opening set alone, setting the tone and cruising away with the match in two confident sets. Seems like MacMillan has worked his magic, right?

How has Coco Gauff improved compared to her previous matches?

Ahead of the US Open, Gauff’s Cincinnati Open run ended in the quarterfinals, falling to Italy’s Jasmine Paolini in a wild three-setter. Paolini rolled her ankle in the decider but still powered through for a 2-6, 6-4, 6-3 victory over the World No. 2. While Paolini showed grit, it was Gauff’s errors that stole the storyline. She piled up an eye-popping 16 double faults and hit just 54% of her first serves, finishing with 62 unforced errors compared to Paolini’s 44. That’s a tough pill to swallow for a player looking to carry momentum into the US Open.

And honestly, this wasn’t the first time Coco’s game looked shaky post-Roland Garros. Earlier in Cincinnati against 18-year-old Victoria Mboko, she coughed up six double faults and 24 unforced errors. It’s a pattern that’s been hard to ignore. Even Rennae Stubbs sounded the alarm on her podcast on August 5. While praising Gauff’s rise, Stubbs admitted, “But my God, like her serve, I don’t understand why now she has literally two coaches. Nothing has changed on her serve…like the ball toss is so far ahead of her on the second serve.” Then came a pointed reminder—Coco brought on Gavin MacMillan, the man who once rescued Aryna Sabalenka’s serve back in 2023.

With MacMillan’s help, the Belarusian marched to consecutive Australian Open finals in 2023 and 2024, lifting the trophy once and hitting a career-high No. 2 ranking. The anticipation was high to see Coco Gauff improve as the US Open rolled around. But her campaign in New York was a grind. A three-set marathon against Ajla Tomljanovic opened her tournament, before Naomi Osaka took her out in the fourth round. The Osaka defeat was painful—five double faults, just 52% points won on first serve, while Osaka fired at 94%. Numbers like that kept the serving question alive, with Stubbs practically begging Coco to find a lasting fix.

Fast forward to now, though, and it feels like progress is finally being made. Gauff confirmed last week at the China Open, “I’m still working with Gavin, but he’s not here because we started last minute, so he had other plans for this part of the year. We’ll be working with each other right when I get home from here.” It’s a positive sign, no doubt. And the timing couldn’t be juicier—up next, she faces fellow American Amanda Anisimova, who’s fresh off back-to-back Slam finals at Wimbledon and the US Open. Title defense on the line, rivalries heating up… can Coco ride this wave all the way to another Slam crown?