How Coco Gauff Fixed Her Serve in a Single Year

A year ago, Coco Gauff’s serve had become one of the most talked-about liabilities in women’s tennis. That led her to change coaches just days before last year’s US Open. The move was highly scrutinized, with Gauff betting her season on a biomechanics specialist rather than sticking with what had already won her a Grand Slam. However, at this year’s US Open, that bet finally started to pay off, and her once-shaky serve is now looking more like a weapon.

Gauff’s Breaking Point in 2025

Gauff arrived at last year's US Open in the midst of a genuine crisis with her serve. She had already suffered a shocking first-round exit at Wimbledon as the No. 2 seed, and entered New York with more than 300 double faults on the season, by far the most on tour.

Her low point came during a second-round win over Donna Vekic, when she committed eight double faults and broke down in tears on the changeover, covering her face with a towel. “I have bad days, but I think it’s more about how you get up after those bad moments,” she said afterward.

Just days before the tournament, she parted ways with coach Matt Daly. She brought in biomechanics specialist Gavin MacMillan as a replacement, calling the decision “very sudden” but necessary for the long term. MacMillan was the same coach who had previously helped Aryna Sabalenka work through her own serving troubles, lending phenomenal results.

The old version of Gauff’s serve had been moving toward a breaking point for a while. The year before, she was eliminated in the fourth round of the 2024 US Open by fellow American Emma Navarro, a loss defined by 19 double faults in a single match. “Obviously, I wish I could serve better. I think if I would have done that, it would have been a different story for me in the match,” Gauff said.

What Changed With Gauff’s Serve

MacMillan’s work with Gauff focused on specific mechanical fixes. One major change was making Gauff’s toss more consistent, correcting a tendency to throw the ball too far forward, and keeping her wrist straighter through the motion. She also lowered her toss and simplified her motion overall, a change she described as necessary even though it was uncomfortable.

Rick Macci, the coach who helped develop Serena and Venus Williams, broke down the changes to Gauff’s serve in detail after studying her motion. He pointed to better use of ground force through her right foot during the loading phase, more efficient rotation through her torso, and a straighter palm position after the toss. These adjustments help her generate a shorter and more explosive swing without sacrificing power.

“Coco and her serve is very different than one year ago. Gavin McMillian a biomechanist in proper efficient throwing mechanics has flipped her script,” Macci said in a post on X. Generally speaking, the goal for improving her serve was simple: fewer moving parts in the motion means fewer chances for something to break down under pressure.

A Newly Rebuilt Serve

It’s now a full season into the MacMillan partnership, and Gauff’s statistical improvement has been noticeable. Her double-fault rate has dropped from roughly 10% in 2025 to 7.9% in 2026. During this year’s North American hard-court swing, she averaged 5.3 double faults per match, down from 9.8 over the same stretch a year earlier.

She’s also seen an improvement in second-serve points won, a stat that speaks to mechanical improvements rather than just fewer mistakes. Gauff described her change in mindset directly ahead of this year’s tournament, saying, “Last year, I literally was like, I hope I make it in. It's such a big difference knowing almost every serve I'm trying to basically hit 110, 115, 120 mph if I can.”

Still a Work In Progress

The overhaul showed up immediately in New York this year, with Gauff winning 93% of her first-serve points in her opening set against Zeynep Sonmez. However, despite the massive strides Gauff has made so far, her serve is still a work in progress.

In her tense quarterfinal escape against Mirra Andreeva at this year’s US Open, Gauff’s old issues resurfaced under pressure. She hit 12 double faults, tied for her second-highest total of the season, and won just 38% of her second-serve points. She managed to escape the match victorious, but her serve looked inconsistent compared to earlier rounds.

Before this year’s tournament began, Gauff referenced her coaching change last season, saying, “I made a big change just before probably the most important tournament of my season, and there was a lot of pressure, but I’m really glad I made the decision.” She continued by acknowledging the improvements herself, “I’m glad I didn't wait another second, because the progress is there and I see it,” said Gauff.

Gauff’s New Confidence

Coco Gauff’s newly rebuilt serve has also affected how she carries herself on the court. Where her old serve became a source of public anguish, this year’s version has let her play with a new level of confidence.

This year, she reached her first US Open semifinal since winning the title in 2023, following a resurgent summer that began with her first title of the season at the Cincinnati Open. Now a year removed from her sudden coaching change, Gauff wields a serve that looks like a real weapon, even if her toughest matches show there’s still more work left to do.

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