CANCUN, Mexico (AP) — U.S. Open champion Coco Gauff double-faulted four times in a row while serving for the second set and wound up losing 6-0, 7-5 to three-time major title winner Iga Swiatek in round-robin action at the WTA Finals on a windy Wednesday night.

Gauff led 4-2 in the second set, then was a game away from forcing a third while serving at 5-4. The teenager from Florida went up 15-love, then dropped the game with the series of double-faults. After the fourth, Gauff spiked her racket, then picked it up and tossed it at her bench as she walked to the sideline.

That was part of a stretch in which the American lost nine points in a row and 12 of the last 13 against Swiatek, who improved to 9-1 against Gauff.

Earlier, Gauff chucked her racket after one errant backhand return late in the lopsided opening set.

That was the 22nd 6-0 set won in 2023 by Swiatek, a 22-year-old from Poland who was ranked No. 1 for nearly 1 1/2 years until Aryna Sabalenka overtook her after the U.S. Open in September. Swiatek is the first woman to win at least 20 sets by a 6-0 score in two consecutive seasons since Steffi Graf and Monica Seles both did it in 1991-92.

Swiatek improved to 2-0 in round-robin play, while Gauff dropped to 1-1. Both will play their last group matches Friday.

The other singles match Wednesday at the season-ending championship — which is for the top eight players in women's tennis — was Wimbledon champion Marketa Vondrousova against three-time major finalist Ons Jabeur.

Gauff and Jessica Pegula, who qualified for the singles semifinals with a victory Tuesday, were scheduled to play doubles against Barbora Krejcikova and Katerina Siniakova in Wednesday's final contest.

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AP tennis: https://apnews.com/hub/tennis