Russian qualifier Veronika Kudermetova pulled off a shock victory over world No.6 Karolina Pliskova to reach the quarter-finals of the WTA’s Ostrava Open.

Pliskova, a former world No.1 and the tournament’s second seed, looked in control after taking the opening set, during which Kudermetova took a medical timeout for a rib problem.

However, the Czech was soon pushed on to the back foot as Kudermetova rallied to level the match before progressing 4-6 6-4 6-3 in just under two hours.

Earlier on Thursday, Ons Jabeur ended the run of former French Open champion Jelena Ostapenko with a 6-4 6-4 win to reach her fifth quarter-final of the year.

Third seed Aryna Sabalenka came from behind to beat American teenager Coco Gauff 1-6 7-5 7-6 (7-2), while Belgian seventh seed Elise Mertens brushed aside Czech player Karolina Muchova 6-4 6-2.

In the day’s late match, Jennifer Brady beat Russian Daria Kasatkina 7-5 6-2, which set the American up for a quarter-final against Kudermetova.