World number three Maria Sharapova slumped to a surprise 6-4, 6-4 defeat against German Angelique Kerber in the Paris Open quarter-finals Friday.
The top-seeded Russian broke first in both sets but failed to take her chances and was eventually eliminated when she hit a forehand out on match point.
"It was a hard day. She played extremely well," Sharapova told reporters.
"I was not as aggressive as I would have liked to be and she has a lot of power," she added.
Sharapova, who reached the final of the Australian Open last month, denied she took Kerber lightly.
"I did not underestimate her. She has been playing very well for six months," said the Russian.
"You would like to be in the final in every tournament you play but let's be realistic, the positive thing is I have the feeling I can play better than this," she added.
Kerber was delighted after beating a top-five player for the first time in her career.
"I played very well. I just played my game, that was my plan," said the ninth-seeded Kerber.
The world number 27 next meets Yanina Wickmayer of Belgium, who beat German Mona Barthel 6-4, 6-7, 6-3 in their late quarter-final clash.
Local hope Marion Bartoli was trailing 4-1 in the second set and 5-2 in the third and needed to show tremendous grit to battle back and beat Italy's Roberta Vinci 4-6, 6-4, 7-6.
The second seed will meet Klara Zakopalova in the last four after the Czech beat sixth seed Julia Goerges of Germany 3-6, 7-5, 6-1.