Dominika Cibulkova of Slovakia reacts after winning her match against Victoria Azarenka of Belarus during the French Open tennis tournament at the Roland Garros stadium in Paris, June 3, 2012. [Photo/Agencies]

PARIS - Victoria Azarenka was knocked out of the French Open fourth round on Sunday and could now lose her world number one ranking.

The top-seeded Belarussian was beaten 6-2 7-6 by Slovakian 15th seed Dominika Cibulkova and must wait to see if Russian Maria Sharapova will claim the top spot.

Sharapova, who meets unseeded Czech Klara Zakopalova in the last 16 on Monday and has yet to drop a set here, must get to the Roland Garros final for the first time to become number one.

Cibulkova, who reached the French semi-finals three years ago and had lost seven times to Azarenka in eight previous meetings, collapsed on to her back, a big grin on her face, after winning the tiebreak 7-4 with a backhand crosscourt on her second matchpoint.

The Slovakian will play US Open champion Samantha Stosur of Australia in the quarter-finals.

Victoria Azarenka of Belarus wipes her face during her match against Dominika Cibulkova of Slovakia during the French Open tennis tournament at the Roland Garros stadium in Paris, June 3, 2012. [Photo/Agencies]

Asked how she would recover from the defeat, a stone-faced Azarenka said sarcastically: "I'm going to kill myself!"

Analysing what went wrong, she said: "Pretty much everything, really. I don't know how to describe my performance today...I wasn't satisfied being out there playing that way but I guess it happens."

Italy's Sara Errani saw off her second French Open champion in two rounds when she beat Russian Svetlana Kuznetsova 6-0 7-5 to reach the quarter-finals of the claycourt grand slam for the first time.

"I am curious to see how far I can go, what level I can get to," said clay specialist Errani, who had knocked out Serbian Ana Ivanovic, the 2008 winner, in the previous round.

Sunday's matches were played under cloudy skies and Kuznetsova, who won in 2009, said the gloomy weather had affected her.

"Today the weather was so bad. I felt cold during the whole match. For me to move was really complicated, I couldn't make my feet move," said the Russian who started working with Marat Safin's old coach Hernan Gumy a week before the tournament.

Errani will now play another first-time quarter-finalist here, 10th seed Angelique Kerber who beat Croatian Petra Martic 6-3 7-5 on Suzanne Lenglen Court.

The Italian said she would change her tactics to play left-hander Kerber but, pressed on what she would do, told reporters with a smile: "I am not telling you for now, I am keeping it to myself."

Dominika Cibulkova of Slovakia (front) shakes hands with Victoria Azarenka of Belarus after winning her match during the French Open tennis tournament at the Roland Garros stadium in Paris, June 3, 2012. [Photo/Agencies]