Ostrava (Czech Republic),  Two days after scoring the first Top 20 win of her career, qualifier Alycia Parks on Thursday notched her maiden Top 10 victory, upsetting No 4 seed Maria Sakkari 5-7, 7-5, 7-5 at the Ostrava Open to reach a WTA Tour quarterfinal for the first time, here.

No 144-ranked Parks had knocked out former World No 1 Karolina Pliskova in straight sets in her opener. The same formidable power was also on display against Sakkari as Parks tallied 59 winners, including 15 aces, while keeping her unforced error tally down to 26. By contrast, Sakkari managed only nine winners throughout.

However, the 21-year-old Parks -- who is in Ostrava alone, with her team back at home in Florida -- also demonstrated superb resilience to come from behind and weather several nail biting moments en route to a 2-hour, 44-minute victory.

"I came out here not expecting anything, just playing my game, and it got me through the match," said Parks, who also expressed an affinity with the Ostrava courts.

"I was coming from Parma last week, and everyone said, how are you going to switch surfaces like that? But surfaces don't really affect me. Indoor hard is my strength," she added.

As both players settled into the match, they exchanged breaks in the first two games. At 5-5 in the first set, a pair of Parks double faults opened the door for Sakkari, who came up with some superb passing shots en route to the crucial break. But Parks was able to shake off the disappointment of losing such a tight opening act, keeping the match competitive with some emphatic holds.

As the match went on, Parks' prowess at net became crucial. A brilliant stab volley staved off a breakpoint at 4-4 in the second set, and she went on to break Sakkari after a three-deuce tussle in the final game of the set.

In the decider, it was Sakkari's turn to escape at a similar juncture as the Greek player saved four break points to hold for 4-4. But Parks came up with some of her finest shots of the day to keep her nose in front, and pounced again at 6-5. Errant Sakkari forehands gave her an opening, and Parks converted her first match point with a searing forehand winner on the line.

Parks will next have a first-time meeting with former Roland Garros champion Barbora Krejcikova, who advanced via walkover after No.6 seed Belinda Bencic withdrew due to a left foot injury.

Krejcikova has battled injury and illness throughout 2022, falling out of the Top 20 from a career-high of No 2. However, the Czech has returned to form this month and is now on a six-match winning streak following a top-quality title run in Tallinn last week.