TOKYO — Aliaksandra Sasnovich produced the biggest upset of the Pan Pacific Open on Thursday, ousting third-seeded Karolina Pliskova in straight sets to advance to the quarterfinals.

Sasnovich, of Belarus, beat the U.S. Open finalist 6-4, 6-2 for her first win over a top-10 player. She will face local favorite Naomi Osaka in the next round.

“I was expecting now to be going to Wuhan for the next tournament because I know Karolina is a really good player and I didn’t expect to win today,” Sasnovich said. “But, you know, it’s life and it’s tennis. The ball is round.”

Top-seeded Garbine Muguruza also advanced with a comfortable 6-3, 6-3 win over Anastasija Sevastova.

Muguruza, who lost to Sevastova in the second round of the U.S. Open, broke her opponent five times to set up a quarterfinal with Elina Svitolina. She beat eighth-seeded Anastasia Pavlyuchenkova 7-6 (5), 6-4.

“Maybe there was a little bit of pressure,” Muguruza said. “But I’m so happy that I came back as top seed, because it means that I’m improving and hopefully I can be in the final.”

Also, Magda Linette saved two match points to defeat Yulia Putintseva 4-6, 6-3, 7-5.