World number one Amelie Mauresmo pulled out of the Zurich Open with a shoulder injury on Friday.

Fourth seed Elena Dementieva also said goodbye to the tournament, losing 6-1 6-4 to unseeded Katarina Srebotnik of Slovenia, and eighth seeded Italian Francesca Schiavone joined Mauresmo on the injury list, retiring with a calf strain after losing the first set 6-1 to Swiss qualifier Timea Bacsinszky.

Second seed Maria Sharapova struggled for over two hours to get the better of Israel's Shahar Peer, the Russian eventually progressing with a 6-4 7-6 win.

Third seeded Russian Svetlana Kuznetsova also had to fight hard to overcome Jelena Jankovic of Serbia, earning a 7-6 7-5 victory and a quarter-final meeting with Martina Hingis.

Mauresmo, who had been due to play Daniela Hantuchova of Slovakia in the quarter-finals, said the injury could jeopardise her defence of the WTA Championship title in Madrid next month.

"I hope I will be in Madrid," the Frenchwoman told reporters. "I can't say for sure today that I'm going to be but I'll do my best and hopefully it will work."

The shoulder had hampered Mauresmo in the second round on Wednesday when she hit five double-faults as she struggled to beat Australian Samantha Stosur 7-6 6-3.

Dementieva had beaten Srebotnik six times in six meetings before Thursday, although the last three had ended in tightly-contested third sets.

Their most recent match came in Stuttgart two weeks ago, when Dementieva collapsed with leg cramps before winning the three-hour battle. The Russian was affected so badly, however, that she was unable to play her next match two days later.

Fears of another marathon were obviously on her mind and Dementieva said: "I think I didn't have enough patience today. I was going for the winners. I didn't want to play long rallies and I made too many mistakes."

Kuznetsova failed to win four set points at 5-4, held off three set points in the first set tiebreak and then recovered from 3-5 in the second set to overcome Jankovic in a match marred by a number of controversial line calls that infuriated both players.

Sharapova, playing for the first time since withdrawing from a tournament in Moscow last week with a foot injury, committed a succession of forehand errors against an opponent who ran down every ball and battled strongly all the way.

In the second set, Sharapova faced a set point at 5-4 which she held off with a service winner, broke for 6-5 but failed to serve out the match, and then took the tiebreak 7-4.

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