After glimpses of revival in late 2024 and early 2025, Coco Gauff’s serving demons have stormed back with fury. At the WTA 1000 Canadian Open in Montreal, she piled up 42 double faults in just three matches, nearly gifting away a set’s worth of points against Danielle Collins. Though her relentless fight carried her through, the warning signs blazed bright: without a stable serve, her ceiling remained capped. In response, Gauff cut ties with grip expert Matt Daly, hired after last year’s US Open, and turned to biomechanics guru Gavin MacMillan, the mastermind credited with rescuing Aryna Sabalenka’s once-broken serve. But who exactly is he?

Gavin MacMillan’s journey into the world of tennis and sports science is anything but ordinary. Growing up in Toronto, his earliest obsession was hockey, before dabbling in the same high school sports as everyone else: basketball, volleyball, and endless running. But destiny had other plans. 

Pushed out of hockey by his father, he was redirected toward tennis and soon found himself at the All-Canadian Tennis Academy in London, Ontario. That twist of fate set him on a new course, one that would eventually intersect with Coco Gauff.

By the age of 16, MacMillan had already begun chasing a different dream. His raw athleticism and sharp instincts earned him a tennis scholarship to San Jose State University. Years later, in 2001, he founded the Sport Science Lab, a hub dedicated to biomechanics and performance innovation. His reputation grew steadily, but his most visible breakthrough came when he helped world No. 1 Aryna Sabalenka rebuild her broken serve into a weapon feared across the WTA.

Now, that same expertise has brought him to Coco Gauff’s corner. Cameras captured MacMillan courtside in Arthur Ashe Stadium this week, guiding Gauff through practice alongside JC Faurel, another key figure in her team. For fans, it was the first glimpse of a potential partnership built on precision, science, and trust.

“A lot of things add up and this could be a really good relationship,” ESPN’s Darren Cahill observed on air. “He’s very thorough … I’ve spoken to him many, many times before and the fact that he’s got experience with different athletes from different sports, both male and female, he uses the new technology, he goes to the video a lot, really breaks down the biomechanics.”

Still, Gauff arrives in New York with a mixed form. She is 4-4 since winning Roland Garros and most recently fell to Jasmine Paolini in the Cincinnati quarterfinals. That uneven stretch has left analysts questioning her confidence.

“It’s crazy how quickly you can lose your confidence,” ESPN’s Mary Joe Fernandez reflected. “You win a Grand Slam title and you think you’re riding this wave and it’s going to carry over and it doesn’t always happen.” 

Yet, while many see her latest move as breaking news, the real story may be that Coco Gauff’s song at the US Open is only just beginning.

Coco Gauff drops surprise last-minute US Open announcement

Coco Gauff recently lit up her Instagram with a powerful announcement ahead of the US Open, unveiling a fresh chapter in her partnership with Baker Tilly, a global advisory, tax, and assurance firm. The young star, already carrying the weight of American hopes, shared glimpses of her New York preparations alongside the caption: “Together with @bakertillyus, we’re redefining what’s possible. Ready to meet the moment in New York.” It was both a statement of intent and a reminder of her growing influence beyond the baseline.

Her bond with Baker Tilly first sparked in 2023, when she was named the brand’s ambassador. At the time, her rise was meteoric, her appeal magnetic, and Baker Tilly saw in her the perfect reflection of ambition and global reach. The then CEO Alan Whitman lauded her, saying: “Coco Gauff is a trailblazer whose quiet confidence and steely courage are riveting to watch. We are proud and honored to partner with Coco. She is a role model with a worldwide following who inspires us all to reach for what’s possible.”

Now, that partnership takes on fresh energy at the year’s final Slam. For Baker Tilly, the collaboration opens the door to a wider audience; for Gauff, it underscores her stature as both athlete and global brand.

But beyond the endorsements lies the bigger question: can Gauff’s serve hold firm in New York? With biomechanics specialist Gavin MacMillan now in her corner, hope surges that her long-standing Achilles heel may finally be tamed.

If that happens, Gauff won’t just meet the moment in New York; she could ignite it, carrying American dreams on her shoulders and chasing a legacy written in fire and resolve.