Li Na's hopes of defending her French Open title were ended with a 3-6 6-2 6-0 defeat by world number 142 Yaroslava Shvedova in the fourth round.

Li, who beat Francesca Schiavone in the 2011 final, struggled with the cool and windy conditions as Shvedova's greater consistency proved the difference.

The Kazakh qualifier next faces Wimbledon champion Petra Kvitova or American Varvara Lepchenko.

Maria Sharapova stumbled past Klara Zakopalova 6-4 6-7 (5-7) 6-2.

Match stats

The second seed made 53 unforced errors in a match featuring 21 breaks of serve in 30 games.

But she made it through unlike Li , who joins Victoria Azarenka, Serena and Venus Williams, Caroline Wozniacki and Agnieszka Radwanska among the big-name casualties.

The seventh seed from China - Asia's first Grand Slam singles champion - was bidding to become the first woman to successfully defend the Roland Garros title since Justine Henin in 2007.

But after a confident start on Court Suzanne Lenglen, the 30-year-old endured a spectacular meltdown in the second set and never recovered.

She finished with 41 errors and was broken seven times by her 24-year-old opponent, 2010 doubles champion at Wimbledon and the US Open.

"I will take some days off to totally forget tennis, then try to come back next week" said Li, who hasn't won a title since her Paris triumph 12 months ago.

"I need some time to recover, I'm not a machine. I just tried to play the ball back to the court, but I couldn't. I will find out why. But not today."

Sharapova continues her bid to win a maiden French Open title against Kaia Kanepi or Arantxa Rus on Wednesday.

But she will hope for a vastly improved display after labouring past Zakopalova in three hours and 11 minutes, with 12 double-faults.

"She played extremely well, she's a dangerous player," said Sharapova, who will become world number one if she reaches the final.

"The conditions were difficult today, but it was a good test for me. I had the chance to finish it in two. I came out strong in the third set and it's nice to be in the quarters again."

Zakopalova fought back from 5-2 to 5-4 in the first set but Sharapova held firm before moving 3-1 ahead in the second.

The 42nd-ranked Czech twice prevented her opponent from serving out the match and edged the tie-break when Sharapova blazed wide.

Sharapova seemed to be having problems with her right wrist but that did not stop her winning the first three games of the decider.

The Russian failed to serve out at 5-1, but was gifted it in the next game when Zakopalova ended the contest with a double-fault.