The Bank of the West Classic took yet another strange turn Thursday, with Varvara Lepchenko, ranked No. 60, beating top seed and fifth-ranked Caroline Wozniacki, 6-4, 6-2, at the Taube Family Tennis Stadium.
Moving into Friday's quarterfinals, half of the seeded players have been eliminated. More than half if you include world No. 1 Serena Williams, who was forced to withdraw just before the tournament draw.
Second-seeded Agnieszka Radwanska also had a difficult match, rebounding from a first set loss to beat qualifier Misaki Doi, 1-6, 6-2, 6-0. In other matches, fifth seed Angelique Kerber topped Ana Konjuh, 6-3, 6-4; and fourth-seeded Karolina Pliskova tripped up qualifier Kimiko Date-Krumm, 7-5, 6-2.
Lepchenko not only endured Wozniacki, she had to put up with four brief rain delays in the second set.
"I felt the sky didn't want me to win," Lepchenko said. "Every time I would get some momentum, start going for winners, it would start raining. It was like a roller coaster. It's OK to rain but not every other game."
Lepchenko, who beat 49th-ranked Mirjana Lucic-Baroni on Tuesday, meets 63rd-ranked Mona Barthel on Friday afternoon.
"At the beginning of the year, I was sick and kept pushing through," Lepchenko said. "After Wimbledon, I decided to take some time to get myself back into condition. I was feeling pretty good and I thought I might have a chance to beat her. Coming back here every year gives me confidence."
Wozniacki made her Stanford debut.
"Physically I wasn't 100 percent," Wozniacki said. "I still thought I had enough to play and beat her. The ball was coming at me so fast I couldn't get into a rhythm. It wasn't pretty out there, that's for sure."
The 60th-ranked Lepchenko reached the quarterfinals after failing to get out of the first round in her last seven events. She beat a top-20 opponent for the first time this year and knocked off a top-five opponent for the third time in her career.
The seventh-ranked Radwanska, playing for the first time since the Wimbledon semifinals, was down 0-2 in the second set before rattling off 12 consecutive games to set up a meeting with fifth-seeded Angelique Kerber in Friday's quarterfinals.
"It was just a weird match with such a slow start and then winning 12 games in a row," Radwanska said. "The ball was flying a lot and I really didn't practice much the last few days. For me, it was a new start, new courts, new balls and a new tournament."
Fourth-seeded Karolina Pliskova of the Czech Republic topped Japanese qualifier Kimiko Date-Krumm, at 44 the oldest player on the tour, 7-5, 6-2.
"She plays so cleverly," Pliskova said. "I get the feeling she could play the next five years. I was expecting a tough match and the first set was really tough."
The top-seeded doubles team of Hao-Chun Chan and Yung-Jan Chan were also upset. The duo of Kateryna Bondarenko and Tatjana Maria took care of business with a 2-6, 6-2, 10-7 victory.
In other doubles matches, Yi-Fan Xu and Saisai Zheng defeated Barthel and Sabine Lisicki, 3-6, 6-4, 10-5; and Gabriela Dabrowski and Alicja Roloska beat Asia Muhammad and Ajla Tomljanovic, 6-4, 6-2.