Top seed Caroline Wozniacki crashed out of the French Open in a shock 6-1 6-3 loss to 28th seed Daniela Hantuchova.
The 20-year-old world number one, who is still yet to win a Grand Slam, lacked the power to trouble Hantuchova.
Wozniacki did rally from 0-4 to 3-4 in the second set but she could not stop Hantuchova from setting up a fourth-round clash with Svetlana Kuznetsova.
Last year's runner-up Sam Stosur also bowed out, suffering a surprise 6-4 1-6 6-3 defeat against Gisela Dulko.
But defending champion Francesca Schiavone went through to the last 16 when 29th seed Peng Shuai of China retired because of breathing difficulties, with the Italian leading 6-3 1-2.
Schiavone will play Jelena Jankovic, who beat Bethanie Mattek-Sands 6-2 6-2.
Wozniacki, who has won four titles this season, never looked comfortable on the clay and struggled to impose herself against her Slovakian opponent.
The Dane did not manage a single winner until the second game of the second set and was unable to live with the precision and pace of Hantuchova's groundstrokes.
Hantuchova has had problems closing out matches in the past and did let Wozniacki back into the match, even though the Dane broke back during a three-game run midway through the second set.
Wozniacki was unable to trouble Hantuchova's serve again, and her fate was sealed when she flopped a forehand into the net to hand her opponent victory in only 73 minutes.
"She played very, very well today, better than me for sure," said the Dane. "She knew what she was going out there to do. She was just too good."
On her continuing wait for Grand Slam success, she added: "I don't feel the pressure. The only one I feel pressure from is myself to go and give my all for every match and obviously I'm a competitor - I love winning. I don't like losing."
"I get so many questions about the depth of the women's game, if you deserve it [the number one ranking], all these kind of things. I know that everyone has to write a story, but tennis is a sport where only one can win. There are no ties. You cannot go off the court and both of the players are happy."
A delighted Hantuchova said: "I was very confident before the match because the last few weeks I think I was playing great tennis, and I was a little bit unlucky in a few matches.
"I knew it was just a matter of time. I have to say today was probably one of my best matches."
Stosur was also left to rue a disappointing display, with a rash of unforced errors proving costly against Dulko, who has never gone beyond the fourth round in a Grand Slam.
Dulko was soon 5-2 up in the opening set and, although she missed set points in the next two games, she did not squander her third opportunity.
Stosur appeared to have turned things around in the second set, and when she broke to go in front at the start of the third she was on track for a place in round four.
But from there the Australian fell apart and Dulko did not have to do much more than keep the ball in play to secure a place in the fourth round for the first time since 2006.
Peng made a superb start against Schiavone, hitting the ball cleanly and covering the Suzanne Lenglen Court in intrepid fashion.
She had three break points to win Schiavone's opening service game but did so at the next opportunity when the Italian netted a backhand.
However, Schiavone soon began to find her touch, opening her shoulders to unleash some powerful groundstrokes.
With three break points to level, she did so at the third attempt courtesy of an overhead smash down the line from baseline.
Schiavone broke to love as Peng's game began to falter and though the Chinese player had a break point to reduce the gap to one game, it was the Italian took the opening set in 54 minutes.
Peng hit a superb backhand down the line to clinch the first game of the second set but had been coughing continuously and showing signs of breathing problems and the doctor was called to the court.
However, it was Schiavone whose concentration suffered and she grew frustrated by the perpetual delays.
Finally, Peng decided to quit and, to sympathetic applause from a crowd who had been enjoying a well-balanced contest, the 25-year-old left the arena.
Also on Friday, 11th seed Marion Bartoli fought back from a set down to see off rising German star Julia Goerges 3-6 6-2 6-4 and reach the fourth round at Roland Garros for the first time since 2007. The 26-year-old French number one has never been further than the last 16 in Paris.
Kuznetsova, the 2009 champion, had little trouble continuing her progress, brushing aside Canada's Rebecca Marino 6-0 6-4 in only 49 minutes.
Third seed Vera Zvonareva enjoyed a 6-2 6-3 win over Anastasia Rodionova in 87 minutes, even though the Australian hit more winners - 19 compared to the Russian's 16.