NEW YORK (AP) — Coco Gauff dealt just fine with the heat, the humidity, her big-hitting opponent and the task of trying to reach the US Open semifinals for the first time, defeating 2017 French Open champion Jelena Ostapenko 6-0, 6-2 on Tuesday.

Gauff, a 19-year-old from Florida, is the first American teenager to reach the final four at Flushing Meadows since Serena Williams was the runner-up to her older sister, Venus, in 2001.

“Last year, I lost in the quarterfinal stage, and I wanted to do better this year,” Gauff said. “Still have a long way to go, but I’m happy and I’m ready to get back to work for the next one.”

This was the 16th victory in her past 17 matches for Gauff — a first-round exit at Wimbledon in July sure feels like ages ago. Her best Grand Slam showing so far was making it to the final at Roland Garros last year.

Gauff lost that title match to Iga Swiatek and those two could have met again in the US Open quarterfinals. But Swiatek didn’t make it, instead losing to Ostapenko in the fourth round. That defeat not only ended Swiatek’s title defense but also meant she will relinquish her spot at No 1 in the WTA rankings to Aryna Sabalenka next week.

When she is on the mark, as she was Sunday night against Swiatek, Ostapenko can be as challenging an opponent as there is, because she goes for broke on nearly every stroke. If the balls land in, she is in business. When they don’t, she is in trouble. She finished with 36 unforced errors Tuesday; Gauff had 14.

“I didn’t feel comfortable at all the whole match, even on match point. I know the game she plays. She has the ability to come back, no matter the scoreline,” said Gauff, who lost to Ostapenko at the Australian Open in January, “so I was just really trying to get every point, trying to play every ball.”

In the semifinals Thursday, Gauff will face No 10 Karolina Muchova of the Czech Republic or No 30 Sorana Cirstea of Romania. They were scheduled to play Tuesday night.