NEW YORK -- Coco Gauff raised a fist, then wagged her right index finger, responding to, and riling up even more, a loud-louder-loudest Arthur Ashe Stadium crowd that was standing and screaming. Gauff's U.S. Open opponent, Zhang Shuai, covered both ears with her hands to shield them from what she described later as a "Boom!" of sound.
Gauff and her fans were reacting excitedly to quite a point, one in which the 18-year-old Floridian raced to her right for a defensive forehand, then changed directions to sprint and slide into a backhand that drew a netted volley from Zhang. Just four points later, Gauff was a quarterfinalist at Flushing Meadows for the first time.
Gauff, the French Open runner-up in June, came back in each set to beat China's Zhang 7-5, 7-5 on Sunday to become the youngest American to make it this far at the U.S. Open since Melanie Oudin was 17 in 2009.
"Here, I can't hear myself scream. Makes me want to do it more. I think I'm feeding off the momentum a lot. I enjoy it," said No. 12 seed Gauff, who meets No. 17 Caroline Garcia of France on Tuesday. "New York is bringing out a side of me that I haven't had since I was 15, so it's nice."
Nick Kyrgios is playing much better than he ever has at Flushing Meadows, too, building off the momentum of his run to the Wimbledon final in July, and he eliminated defending champion and No. 1-ranked Daniil Medvedev 7-6 (11), 3-6, 6-3, 6-2 on Sunday night.
The 23rd-seeded Kyrgios was up to some of his usual behavior -- warned for cursing, yelling at his guest box, playing to the crowd -- but he also outplayed Medvedev in a high-quality match.
"I'm just glad I'm finally able to show New York my talent," said Kyrgios, never past the third round at the U.S. Open until now. "I haven't had too many great trips here."
He'll play No. 27 seed Karen Khachanov on Tuesday, when the other's men's quarterfinal on the top half of the bracket is 2022 French Open runner-up Casper Ruud against 2021 Wimbledon runner-up Matteo Berrettini.
Medvedev will relinquish the top spot in the rankings after the U.S. Open, with Ruud joining Rafael Nadal and Carlos Alcaraz as players with a chance to replace him.
After trailing 5-4 in the opening set, then 5-3 in the second, which she was a point from losing, Gauff was buoyed by spectators who cheered her every point and chanted "Let's go, Coco!" as the end neared. She improved to 4-0 in Ashe this year after having never previously won a match at the biggest arena in Grand Slam tennis.
How loud was it?
"It got so raucous in there that I got a headache. I had to take an Advil," said Gauff's father, Corey. "I kept pinching myself. I'm like, 'My gosh, all of these people here for my daughter.' You dream about this, but you never know if you're going to realize that. She was pumping herself up and they responded to her. It sent chills up my spine."
Zhang, at 33 the oldest woman to reach the fourth round, said it was more noise than she's ever heard at a match.
She praised Gauff's play, calling her "a superstar" and adding: "Everything is very good. She's so much younger than me. Her energy is so much better. She's faster. She's powerful."
They competed mostly from the baseline, and the longer the exchanges, the more success Gauff found: She claimed a 45-26 edge in points that lasted five or more strokes.
Garcia is coming off a hard-court title at Cincinnati and stretched her winning streak to 12 matches by defeating No. 29 Alison Riske-Amritraj of the U.S. 6-4, 6-1.
"I'm super excited, actually, to play Coco -- in U.S., in New York, quarterfinal of a Slam. It's great," Garcia said.
None of the eight women in action Sunday had ever been past the fourth round at Flushing Meadows; only two have reached semifinals at any Grand Slam tournament: Gauff and No. 5 Ons Jabeur.
Corentin Moutet, of France, does push ups on the court after missing a return to Casper Ruud, of Norway, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Eduardo Munoz Alvarez)
Matteo Berrettini, of Italy, celebrates after winning a point against Alejandro Davidovich Fokina, of Spain, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Alejandro Davidovich Fokina, of Spain, returns to Matteo Berrettini, of Italy, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Matteo Berrettini, of Italy, signs autographs for fans after defeating Alejandro Davidovich Fokina, of Spain, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Matteo Berrettini, of Italy, reacts after defeating Alejandro Davidovich Fokina, of Spain, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Caroline Garcia, of France, left, is congratulated by Alison Riske, of the United States, after victory during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Caroline Garcia, of France, celebrates after defeating Alison Riske, of the United States, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Julia Nikhinson)
Coco Gauff, of the United States, celebrates after defeating Shuai Zhang, of China, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Eduardo Munoz Alvarez)
Shuai Zhang, of China, reacts during a match against Coco Gauff, of the United States, during the fourth round of the U.S. Open tennis championships, Sunday, Sept. 4, 2022, in New York. (AP Photo/Eduardo Munoz Alvarez)