- Top-ranked Victoria Azarenka beaten in last-16 clash by Slovakia's Dominika Cibulkova
- World No. 1 loses to the 15th seed for only the second time in nine encounters
- Cibulkova, a semifinalist in 2009, will next face U.S. Open champion Sam Stosur
- German 10th seed Angelique Kerber also in last eight along with Italy's Sara Errani
World No. 1 Victoria Azarenka plans to take a break from tennis following her shock fourth-round defeat at the French Open on Sunday.
The 22-year-old, who lost 6-2 7-6 (7-4) to 15th seed Dominika Cibulkova, said she was jaded after the opening months of the season in which she won her first grand slam at the Australian Open and went on a 26-match winning streak.
However, the Belorussian lost in finals in Stuttgart and Madrid before pulling out ahead of a second-round clash against the diminutive Cibulkova in Rome last month due to a shoulder injury.
She will lose the top ranking if Rome champion Maria Sharapova can reach the final in Paris for the first time in her career.
"There has been a lot of tennis for me in the last five months," she said. "I haven't been home in a while, and it's something that I need just to get rested mentally, definitely, and just to get out of the tennis field a little bit.
"And once I have my passion and desire back on the court, I'll be on the grass."
Azarenka had previously lost to the Slovakian just once in eight meetings, but five of those had gone to three sets and two were remarkable comeback victories.
She had to come from a set and 4-0 down in her opening match in Paris last Monday, but could not pull off an escape this time as she smashed two rackets in frustration.
"Today I couldn't do it. It was just not going for me. I tried everything. All I could hope for was her mistakes," Azarenka said.
"I think she plays much better against the top players than maybe a little bit lower-ranked players. She really has that desire. I don't know what motivates her to play that way."
Cibulkova reached the French Open semifinals in 2009, but said she was nervous she would again blow her advantage against Azarenka -- who stands nine inches taller at six foot.
"You can't be human if you weren't thinking about that," she said. "Because this year in Miami I was 6-1 5-2 up against her. And last year in Miami it was the same.
"Today it happened the same when I was 4-2 up. And that's why I got a little bit ... not nervous, but not going for my shots anymore.
"But today it was a great thing that I managed to go through these emotions. She was 6-5 up, and I said, 'Hey, come on, you have to play your game again and just make it.' "
The 23-year-old will next face U.S. Open champion Sam Stosur of Australia, who beat 79th-ranked American teenager Sloane Stephens.
Sixth seed Stosur, the French Open runner-up in 2010, ended the 19-year-old's dream run as she won 7-5 6-4 in 85 minutes.
Stephens lost in the first round last year and has not won a match in three attempts at her home grand slam.
Italy's Sara Errani earlier reached the quarterfinals after beating 2009 French Open champion Svetlana Kuznetsova.
The 21st seed, who also made the last eight in Melbourne in January and has won three clay titles this season, won 6-0 7-5 to set up a clash with Angelique Kerber.
The German 10th seed, who lost to Stosur in the New York semifinals in September in her best grand slam achievement, ended the hopes of 21-year-old Croatian Petra Martic as she won 6-3 7-5 on Court Suzanne Lenglen.