Kasatkina trailed 4-1 in the first set but rallied to win the opening frame in a tiebreak, before dominating the second set to win 7-6 (8-6) 6-3 in one hour and 40 minutes.
The victory is Kasatkina’s 41st of the year and 25th on the hard-court surface this season. Kasatkina is 29-0 this season when she wins the first set.
Gauff has now suffered two singles losses and two doubles defeats in Fort Worth this week, producing an erratic performance, where she committed 34 unforced errors compared to the Russian’s 10.
Kasatkina had to earn the victory, with the first set lasting 66 minutes, as the eighth seed rallied from 3-0 down in the tiebreak to take the frame with her third set point.
The second set was more dominant, with Kasatkina claiming it in 35 minutes, although it included five straight broken games. Kasatkina converted her first match point from another Gauff error.
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