NEW YORK (AP) — The second set was slipping away from Coco Gauff in the U.S. Open’s fourth round on Sunday, so maybe she was frustrated by that... or the stumble that left her doing the splits while getting broken... or the pair of double-faults that helped Caroline Wozniacki take that game.

Or perhaps it was simply that the last thing she wanted to hear at that moment was the near-constant chatter coming from Brad Gilbert, one of her two coaches sitting in the front row at Arthur Ashe Stadium.

Either way, Gauff turned toward Gilbert and said, “Please stop.” Then, during the next game, which allowed Wozniacki to force a third set, Gauff told him, “Stop talking.”

That was while Wozniacki was grabbing four consecutive games to go up a break in the third set. And then, just as the match seemed to be slipping away thanks in part to a slew of unforced errors, Gauff straightened out her strokes and pulled way. She collected the last six games for a 6-3, 3-6, 6-1 victory over Wozniacki, the 33-year-old mother of two who recently came out of retirement.

During her on-court interview, the sixth-seeded Gauff described the interaction with her entourage as a “stress reaction.”

“Sometimes I tell them to chill a little bit,” the 19-year-old from Florida said, “because I like to think and figure out matches my own way.”

She seems rather adept at that. Gauff became the first American teenager since Serena Williams more than two decades ago to reach the quarterfinals at Flushing Meadows in consecutive years.

In 2022, Gauff lost to Caroline Garcia in that round; this time, the opponent will be defending champion Iga Swiatek or No. 20 seed Jelena Ostapenko. The top-seeded Swiatek was scheduled to face Ostapenko on Sunday night, after 23-time Grand Slam champion Novak Djokovic met qualifier Borna Gojo.

Gauff, whose best showing at a major was reaching the final at the 2022 French Open, has now won 15 of her past 16 matches. That run follows a first-round exit at Wimbledon in July and includes the two biggest titles of her career, at the DC Open and in Cincinnati. It also coincides with the additions of Pere Riba as her full-time coach and Gilbert in a role that’s been described as a temporary consultant.

TV microphones have been picking up Gilbert repeatedly offering his thoughts to Gauff during matches over the past week.

It was the hottest day of the event so far, with the temperature reaching 90 degrees Fahrenheit (32 Celsius), and Gauff kept missing the mark in the second set, to the tune of 22 unforced errors. But she cleaned that up considerably down the stretch, with just eight miscues in the last set.

“She’s always been a great athlete. She’s always had the backhand, the serve, the fighting spirit,” Wozniacki said. “I feel like right now, it’s all kind of coming together for her.”

In the third set, with the playing surface covered in shadows, Wozniacki told chair umpire Louise Azemar Engzell it was difficult to see the ball and requested that the stadium lights be turned on.

“I would really appreciate it,” Wozniacki said.

Didn’t happen. And Wozniacki, the 2018 Australian Open champion and twice a runner-up in New York, was not able to match Gauff stroke-for-stroke down the stretch.

“She’s back and it’s like she never left,” said Gauff, who has won three of her four matches in the tournament in three sets. “To be out here on the court with her today was an honor.”

Another women’s quarterfinal matchup will be No. 10 Karolina Muchova against No. 30 Sorana Cirstea.

Muchova, a finalist at Wimbledon in July, reached the U.S. Open quarterfinals for the first time by beating Wang Xinyu 6-3, 5-7, 6-1. Cirstea hadn’t been to the final eight at any major since the 2009 French Open and got back to that round by defeating No. 15 Belinda Bencic 6-3, 6-3.

There is guaranteed to be at least one American man in the semifinals for the second year in a row. That’s because No. 10 Frances Tiafoe, who got to that stage 12 months ago, and unseeded Ben Shelton set up a quarterfinal meeting with wins Sunday.

A third man from the U.S. had a chance to advance later, when No. 9 Taylor Fritz took on Dominic Stricker of Switzerland.

Tiafoe eliminated Australian wild-card entry Rinky Hijikata 6-4, 6-1, 6-4.

In the day’s first match in Ashe, the 20-year-old Shelton hit a pair of aces at 149 mph (240 kph) — the fastest by anyone all tournament — in a single game and earned a debut trip to the quarterfinals at Flushing Meadows by eliminating No. 14 Tommy Paul 6-4, 6-3, 4-6, 6-4.

When the match ended, the muscle-shirt-wearing Shelton flexed his left biceps while standing under the section of seats where his father, a former touring pro who now coaches Ben, mother and sister were.

“Straight adrenaline,” Shelton said about those big lefty serves.

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