Top-seeded Caroline Garcia lost 12 of the last 17 games to fall to French countrywoman Alize Cornet at the Volvo Car Open on Thursday night.
Garcia, ranked seventh in the world, had a strong opening match Tuesday at the WTA's first clay-court tournament of the season, and she expected to keep that going against Cornet, who entered the week ranked 37th. But Cornet broke serve twice each in the second and third sets to beat Garcia for the second straight time with a 5-7, 6-1, 6-4 victory and move into the tournament quarterfinals.
Garcia had won the first three times the French players had met, including in a round of 16 match at Roland Garros in the French Open last year.
Cornet reached the semifinals here 10 years ago. "I have some great memories from this tournament," she said. "And I'm having an amazing week. I want the journey to keep going as much as possible."
Earlier Thursday, defending champion Daria Kasatkina of Russia, No. 5 Julia Goerges of Germany and seventh-seeded American Madison Keys moved into the quarterfinals with straight-set victories.
Kasatkina, the third seed, moved through with a 6-2, 6-1 win over Romania's Irina-Camilia Begu, the 13th seed. Goerges topped 10th-seeded Naomi Osaka of Japan 7-6 (4), 6-3. Keys, the U.S. Open runner-up last September, beat Italy's Camila Giorgi 6-4, 6-3.
Kastakina said she felt more relaxed on the green clay at the Family Circle Tennis Center than she did in opening play Tuesday.
"Nobody told me it's so difficult to come and defend a title. So I have to get used to it," said Kasatkina, ranked 12th in the world.
Keys needed three sets Wednesday night to take her opening match. She was much more focused in defeating Giorgi. Keys win sets up an all-U.S. quarterfinal against Bernarda Pera, who ousted Italian veteran Sara Errani 6-3, 2-6, 6-4.
Keys says she feels her first two matches have given her confidence, no matter whom she's facing. "I feel like I have pretty good momentum," said Keys, ranked 14th in singles. "I think I served really well today. There was a lot of things that I did well, so I think if I just focus on what I was doing well and what I need to do, then I'm not really concerned about who's on the other side."
Kristyna Pliskova, who entered ranked 77th in the world, knocked off her second straight seeded player in as many days. Pliskova, the twin sister of top-10 player Karolina Pliskova, had beaten Czech Republic countrywoman and two-time Wimbledon champion Petra Kvitova, the No. 2 seed, on Wednesday night. Kristyna Pliskova topped No. 16 seed Elena Vesnina of Russia 6-3, 1-6, 6-2 on Thursday.
No. 8 seed Anastasija Sevastova of Latvia beat No. 9 Ashleigh Barty of Australia 6-3, 6-4, and No. 12 seed Kiki Bertens of the Netherlands defeated Hungarian qualifier Fanny Stollar 6-2, 6-4.