Iga Swiatek, of Poland, returns a shot to Madison Keys at the BNP Paribas Open tennis tournament, March 16, 2022, in Indian Wells, California. (MARK J. TERRILL / AP)

World number one Iga Swiatek qualified for the semi-finals at the WTA Finals in Fort Worth, Texas on Thursday after Daria Kasatkina beat American Coco Gauff 7-6(6) 6-3 in a round-robin stage match at the eight-player, season-ending tournament.

Gauff started the match strongly, roaring to a 4-1 lead, before Kasatkina fought back to level the first set at 5-5. Gauff's eyes welled up with tears during the changeover after she was then broken to fall behind 5-6

Swiatek, who improved to 2-0 in this year's competition following her own 6-3 6-2 win over Caroline Garcia, goes through as the winner of her group, while Gauff can no longer qualify for the semi-finals.

Gauff started the match strongly, roaring to a 4-1 lead, before Kasatkina fought back to level the first set at 5-5. Gauff's eyes welled up with tears during the changeover after she was then broken to fall behind 5-6.

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The 18-year-old regrouped to break back and force a tiebreak, but Kasatkina once again showed grit to fight back from 3-0 down and claim the breaker 8-6.

Kasatkina, a WTA Finals debutante, kept up the pressure in the second set, trading a couple of breaks with Gauff, before breaking to take a 4-2 lead and then serving out the match a few games later.

"To win for the first time at the Finals is an incredible feeling," Kasatkina said.