5-1 to make it six games in a row
Gauff took the first set after going from 2-1 to 5-2 before Kostyuk won two straight games to make it 5-4. The American closed it out 6-4.
The second set went the other way. Kostyuk jumped out to a 4-0 lead and Gauff, who called out the coach for his back, found himself in trouble when he trailed 5-1. But the Ukrainian woman completely lost her way from there. Gauff won six games in a row, closing out the match in 1 hour and 40 minutes.
Gauff now leads them head-to-head 5-2. Suit: Replacement defending champion Elena Rybakinaended his week without a win and has now lost seven matches in a row.
Gaufin needs Noskova to beat Pegula
Noskova has already won her place in the semi-finals. If he beats Pegula, Gauff moves to second place in the group. If Pegula wins, the American takes the second place. Noskova won three of their four meetings, including the Berlin final, 6-4, 4-6, 6-3.
Gauff, the 2024 champion, is chasing her third semifinal at the WTA Finals. The semi-finals are on Saturday.