The 22-year-old went on a 26-match winning streak at the start of 2012, including picking up her first grand slam title at the Australian Open, but she has struggled to find her form all week.
Azarenka almost went out in the first round, fighting back from a set and 4-0 down against Alberta Brianti, but yesterday she could not recover and was beaten 6-2 7-6 (7/4) by the 15th seed.
The Belarusian said: “I don’t know how to describe my performance really today. It wasn’t satisfying at all. It wasn’t satisfying being out the replaying that way. But I guess it happens. I don’t know even what to find positive in my performance today. Maybe in a few hours I’ll find something I can be happy with.”
Despite being only 5ft 3in tall, nine inches shorter than Azarenka, Cibulkova is a talented and feisty competitor and she had far too much for her opponent in the first set.
Azarenka had fought back from significant deficits in her last two matches against the Slovakian, who she had lost only once to in eight previous meetings.
And from 4-2 down in the second set she ended up serving for it only for Cibulkova to break back and dominate the tie-break, clinching victory on her second match point.
Azarenka said: “She’s definitely a good player. 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.
“She’s a dangerous opponent. She had big wins before, and it was no surprise that she was going to be playing well today.”
Azarenka admitted she is mentally jaded after a demanding season and she is not planning to play any grass-court tournaments in the build-up to Wimbledon.
Cibulkova’s best performance in a slam came here in 2009, when she reached the semi-finals, but she admitted the losses to Azarenka had weighed on her mind. “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’.
In the last eight Cibulkova will play sixth seed Sam Stosur, now a hot favourite to reach her second final at Roland Garros. The Australian, who lost the showpiece to Francesca Schiavone in 2010, recovered from 5-3 down in the first set yesterday to beat 19-year-old American Sloane Stephens 7-5 6-4.
Italy’s Sara Errani is through to the quarter-finals of a second successive grand slam after putting out former French Open champion Svetlana Kuznetsova.
Errani, the 21st seed, was too consistent and too smart for 2009winner Kuznetsova, who made far too many errors in the cold and windy conditions, particularly in the first set, before going down 6-0 7-5.
German Kerber, who was outside the top 100 before reaching the semi-finals of the US Open last year, beat Croatia’s Petra Martic 6-3 7-5.