Qualifier Veronika Kudermetova upset second-seeded Karolina Pliskova 4-6 6-4 6-3 to advance to the quarterfinals of the Ostrava Open.
The Russian will face American Jennifer Brady, who eliminated qualifier Daria Kasatkina 7-5 6-2 on Thursday.
Third-seeded Aryna Sabalenka came from two breaks down in the deciding set to eliminate American teenager Coco Gauff 1-6 7-5 7-6 (2).
The 16-year-old Gauff beat Sabalenka in Lexington in August en route to the semifinals and held a 5-2 lead in the third set before Belarusian came back.
"I just need to play a little bit smarter on pressure points, to make my opponent play," Gauff said.
Sabalenka credited Gauff with her forcing her to play long rallies.
"She's 16 and she's playing on this level," Sabalenka said.
"I would like to be on this level when I was 16."
Also, seventh-seeded Elise Mertens beat Karolina Muchova 6-4 6-2 while Ons Jabeur defeated former French Open champion Jelana Ostapenko 6-4 6-4.
The hard-court indoor event was added to the tour after tournaments in China were cancelled due to the coronavirus pandemic.
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