Anastasia Potapova stunned top-seeded Tunisian Ons Jabeur 6-4, 7-6 (7/4) to reach the quarter-finals of the WTA San Diego Open on Wednesday.
Potapova, ranked 27th in the world, said patience was the key against the world number seven, who reached her third Grand Slam final at Wimbledon this year.
"Ons is very tough to play," said Potapova, who had edged Alycia Parks in three sets in the first round as Jabeur enjoyed a first-round bye.
"She is truly one of the best in the world and with her style it's very uncomfortable. I'm really happy and proud to get this win."
Jabeur was coming off a fourth-round showing at the US Open, where she battled illness in the opening rounds.
Potapova notched her sixth career victory over a top-10 player and lined up a quarter-final meeting with 2020 Australian Open champion Sofia Kenin, a 1-6, 6-4, 6-2 winner over fellow American Katie Volynets.
Potapova converted six of her 11 break chances, breaking the Tunisian at love to seal the opening set.
Jabeur served for the second set at 6-5 but was broken, Potapova racing to a 4-0 lead in the tiebreaker before Jabeur bore down to knot it at 4-4.
Jabeur's ninth double fault of the match gave Potapova a double match point, and Jabeur fired wide with a forehand to end it.
Second-seeded Caroline Garcia of France was due to open her campaign later Wednesday in a challenging second-round meeting with Sloane Stephens.
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