American Emma Navarro upset top-seeded Iga Świątek with a 6-4, 4-6, 6-0 win in the fourth round of the China Open on Wednesday.
Navarro, seeded 16th, had not won more than three games in two previous matches against Świątek, who committed 70 unforced errors and lost a love set for the third time this season.
It was the 24-year-old Navarro's fourth career win over a top-five opponent.
Also, Sonay Kartal produced the biggest victory of her career by defeating Mirra Andreeva 7-5, 2-6, 7-5 to reach the quarterfinals. It is the first time Kartal has beaten a top-10 player and the first time she has reached the last eight at a WTA 1000 event.
"I think the way I carry myself on the court is one of my biggest assets. You could look down the other end at me and you wouldn't really know if I'm winning or losing," Kartal said. "I just tried to put that second set behind me. She played some great tennis, so I just tried to level it out in the third set and keep the scoreboard pressure as high as I could."
Fifth-seeded Jessica Pegula later defeated Marta Kostyuk of Ukraine 6-3, 6-7 (4), 6-1, making it the first time since the tournament started in 2004 that four Americans reached the final eight. Compatriots Coco Gauff and Amanda Anisimova had already made the quarterfinals.
Jannik Sinner, playing the concurrent men's tournament in Beijing, won the China Open title by beating American teenager Learner Tien 6-2, 6-2.
The Associated Press and PA contributed to this report.