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 U.S. 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.

This was the 16th victory in her past 17 matches for Gauff — a first-round exit at Wimbledon in July sure seems as if that came 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 U.S. 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.

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

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