Gauff, 19, won 6-0, 6-2 in 67 minutes to post her best tournament performance.

The American dropped only five games in a 20-minute first-set thrashing before winning a tighter second set.

She will face the tenth seed. On Thursday, Karolina Muchova of the Czech Republic will face Romania’s Sorana Cirstea, the 30th seed, in the semi-finals.

“It feels great, and I’m so happy,” Gauff added. “Last year, I lost in the quarter-finals and vowed to do better this year.” I still have a long way to go, but I’m content and will prepare for the next one.

“I didn’t feel at ease the entire match, even at match point.” She has the capacity to come back regardless of the score, so I simply tried to play every ball and smash it far. I was doing my best to be aggressive whenever possible.

“She had a fantastic tournament, and I communicate and get along with her well off the court.”

“The defense has always been there, but I’ve been working on improving my offense, which is showing on the court.”

“I performed admirably. This is by far my quickest match of the tournament, so I might go back and hit the [practice] courts.”

Gauff, who lost to Iga Swiatek in the 2022 French Open final, saw three of her first four matches at this year’s US Open go to a deciding set.

Gauff stormed into a 3-0 lead with a double break of serve after only nine minutes of action in Tuesday’s opening match on Arthur Ashe Stadium, as Ostapenko, who knocked off world number one Swiatek in the last 16, produced 10 unforced mistakes.

Gauff didn’t give up a point on her second serve in the first set and then broke the 20th seed’s service in the first game of the second.

Ostapenko did break back promptly in her first game of the match, only for Gauff to retake control a few minutes later.

Live scores, results, and game order