Coco Gauff left the 2025 US Open with mixed emotions: bruised after a loss to Naomi Osaka but upbeat about the work she has started on her serve. Observers had noted a sombre demeanour during parts of her run in New York, yet Gauff framed the week as part of a broader process.

The changes began after a difficult 2024 North American hard-court swing. She parted ways with Brad Gilbert and joined Matt Daly last September, a partnership that produced immediate results: she won the China Open and finished the year with the season-ending WTA Finals trophy. Her form carried into 2025 with a second major at Roland Garros and runner-up finishes at the Madrid Open and Italian Open, but she acknowledged a persistent weakness in her serve.

When Gavin MacMillan became available after the Cincinnati Open, Gauff made another significant switch. She and MacMillan focused on biomechanics and decided to change her entire service motion. That overhaul left the build-up to the US Open difficult; she described shoulder pain after practice but accepted the short-term discomfort.

A testing three-set win over Ajla Tomljanovic opened her campaign. There were tears during and after a two-set victory over Donna Vekic, and she dropped only four games against Magdalena Fręch in the third round before the defeat to Osaka. After the Fręch match she admitted she “broke down.”

She detailed the emotional swing: “I think that trying to be more positive after the match, I was really disappointed,” she admitted. “Kind of broke down to my team and then hearing their perspectives and everything, it definitely is a lot of positive things.

“If I think if I kept the way I was going in Cincinnati to here, I would have been out the first round. And so I think that where my serve started from the start of the tournament to today was a big improvement. And I feel like now I just have to get everything to work together. But, yeah, I knew going in it was going to be a tough tournament for me.”

Statistically there are signs of progress: she served 320 double faults before the US Open, added 23 in her first three matches in New York and five more against Osaka. “My goal going into the tournament this year was not to lose the same way that I lost last year. And I don’t remember how many doubles I hit in my match against Emma, but it was definitely in the double digits, so I didn’t do that today,” she said.

At 21 she already owns 10 WTA Tour singles titles, including two Grand Slams, a WTA Finals trophy and two WTA 1000 titles, and she has peaked at No 2. With older rivals such as Aryna Sabalenka, 27, and Iga Swiatek, 24, she sees room to grow: “So I think for me, it just gets me excited to realise if I have, like, four more years of just working as hard as I am right now and actually doing the right things, like where my game could be.”

Alexander Bublik’s flair for memorable lines framed the build-up to his latest meeting with Jannik Sinner and provided a lighter moment after a one-sided encounter in New York. Their fourth match of the season ended in emphatic fashion as Sinner prevailed 6-1, 6-1, 6-1.

The pair’s season-long mini-rivalry has swung both ways. At Roland Garros in June Sinner recorded a clinical 6-1, 7-5, 6-0 victory and Bublik later posted on social media: “I almost got him guys.” On grass in Halle the Kazakh reversed the result, winning 3-6, 6-3, 6-4 and quipping after the match: “I got him, guys!”

Before their Arthur Ashe Stadium clash, Bublik was asked what makes Sinner tough to face. “Everything. He is like an AI-generated player, but we all try to find a way to get closer to him, to beat him. I was lucky once and let’s see how it goes today.”

On court, Sinner answered decisively. The match lasted under 90 minutes, leaving little for the crowd to dissect. Bublik had reached the fourth round after a five-set upset over 14th seed Tommy Paul, but he struggled to find rhythm against the world No 1. During the post-match handshake Bublik smiled and said to Sinner: “That’s so good. I’m not bad, but you’re the GOAT.”

Sinner reflected on familiarity and form. “We know each other very well. We had some tough battles, especially this year, so we know each other a little bit better now how we play,” he said. “He just said congrats and wished me all the best. He had a very tough match the last match playing five sets, finishing very late.

“Today he didn’t serve as good as he usually serves, so I broke him very early in every set, which then gave me the confidence to serve a little bit better.”

Sinner’s next opponent is Lorenzo Musetti, who dismissed Jaume Munar 6-3, 6-0, 6-1. The reigning champion leads their head-to-head 2-0, with wins in 2021 and 2023. “It’s great to see. Italian tennis is in great form now. We have so many players, so many different game styles,” Sinner said. “Lorenzo is maybe one of the biggest talents we have in our sport, so I’m looking forward for this one. From an Italian point of view it’s great to have for sure one Italian player in the semis.”

Labor Day at the US Open produced a decisive fourth-round victory as Felix Auger-Aliassime overwhelmed Andrey Rublev, ending a 1-7 deficit in their series. The match on Arthur Ashe Stadium lasted two hours and 16 minutes and finished 7-5, 6-3, 6-4.

Auger-Aliassime, the No. 27 seed and Montreal native, combined blazing serves and a dominant forehand to dictate rallies. Some of his first serves topped 130 mph. He produced 42 winners to Rublev’s 22 while also committing 33 errors to Rublev’s 18. The result gave Auger-Aliassime a quarterfinal berth in a depleted section of the draw, with only No. 8 seed Alex de Minaur standing between him and a place in the semifinals.

“It was a good win considering our head-to-head (Rublev led going in, 7-1) ,considering how good he is as a player,” Auger-Aliassime said. “I was down 4-2 in the first set, but once I settled into the match I felt much better about my chances. From that moment on I felt like I was putting a lot of pressure on him.”

Rublev, the 27-year-old Russian and No. 15 seed, has often reached Grand Slam quarterfinals only to stall thereafter. On this day he could not neutralize Auger-Aliassime’s power or timing. As Sam Querrey said on air, “Rublev has never hit a slice in his life. He’s going to hit hard from either side, every point. If your serve is off and you put the ball right in the pocket he’s going to make you pay. ” Auger-Aliassime simply denied him the chance to make him pay.

Auger-Aliassime reflected on the role of his forehand and his approach: “Well, [the forehand] has always been my strength and my instinct growing up was to have the match be in my hands,” Auger-Aliassime said. “I was never a kid that was playing and waiting for the mistake. Sometimes it played against me. I would miss plenty as a kid, and then I had to kind of know how to use it well, and to be precise and consistent. It’s a similar thing now at a higher level.”

He also acknowledged the process of rebuilding form and fitness: “Throughout the years I still had good moments,” Auger-Aliassime said. “I was around 25, 30 in the world. It was not like I was losing all the time. But for sure there were months where I was thinking, ‘Okay, what’s my approach tactically with my game?’ Once I got the physical (injuries) things kind of sorted out, it was like, ‘Okay, now I’m healthy again. How am I playing?’”

Auger-Aliassime arrives in the quarters having upset No. 3 seed Alexander Zverev in the previous round and having reversed recent major disappointments that included collapses at the Australian Open, Roland Garros and Wimbledon.