Parks continues giant-killing WTA run

The 144th-ranked Parks ousted former No.1 Karolina Pliskova in the opening round - her first win against a top-20 opponent - and showed off her power by hitting 59 winners against Sakkari, compared to just nine for her opponent.

"I came out here not expecting anything, just playing my game and it got me through the match," Parks said.

Parks will next face former French Open champion Barbora Krejcikova, who advanced via walkover when Belinda Bencic withdrew with a left foot injury.

Caty McNally, another American qualifier who is playing doubles with Parks in Ostrava, also reached the last eight by beating wild-card entry Karolina Muchova 6-1 3-6 6-1. 

McNally is also into her first WTA quarter-final and will face top-ranked Iga Swiatek, who advanced Wednesday by beating Australian Ajla Tomljanovic who was forced to retire midway through their match because of a knee injury.