After stunning second-ranked Aryna Sabalenka in straight sets in the third round of the China Open on Sunday, 34th-ranked Nikola Bartunkova's run continues in Beijing.
Bartunkova defeated Sinja Kraus 6-0, 4-6, 6-3 on Tuesday to advance to the quarterfinals.
Bartunkova's victory sets up an all-Czech matchup against seventh-seeded Karolina Muchova, who overcame a second set scare to knock out 12-seed Naomi Osaka 7-5, 1-6, 7-6 (7) in just under three hours. This will be the first meeting between Bartunkova and Muchova.
Despite serving up 11 aces against Muchova, Osaka was unable to capitalize on break point chances, converting just 50% (5-of-10) throughout the match.
"I honestly didn't even believe I will finish the match," Muchova said after the match. "So many match points, I didn't know how many. I was shaking. I'm happy that I made the last volley and it was really so close. Naomi could be standing here. It's me, and I'm really grateful for it."
Wimbledon champion Linda Noskova, the tournament's fifth seed, was upset by 19th-seeded Ekaterina Alexandrova 6-2, 6-2 in just over an hour, with Alexandrova dominating all aspects of the match, including winning an incredible 88% (21-of-24) of points on her first serve.
Noskova struggled throughout the match to find any footing, committing six double faults. She was also 0-for-4 on break point opportunities while being broken four times.
The win moves Alexandrova, ranked No. 25 in the world rankings, into the quarterfinals, where she'll face four-seed Mirra Andreeva, who won the French Open in May.
Alexandrova is 2-0 in head-to-head meetings with Andreeva and has not dropped a set in those two matchups.
Information from the Associated Press was used in this report.