Top seed Williams ousted by Stosur

Seventh seed Stosur, who on Monday became the first woman to beat Justine Henin at the event for six years, held off a tremendous fightback by Williams – who had match point – to win 6-2 6-7 (2/7) 8-6.

The Australian, who lost to eventual champion Svetlana Kuznetsova in the last four last year, will now play Jelena Jankovic for a place in the final.

For 2002 champion Williams, it was another quarter-final defeat at Roland Garros, which she had been a strong favourite to win being the only grand slam champion left in the draw.

"It was my match and I lost it. That's basically what happened," said the 28-year-old, who cut a frustrated figure for much of the contest. "I didn't play well, I don't think at all, from literally the first point.

"I was more or less upset that I was able to play so well up until this point. I just couldn't believe that I played like that."

In the men's draw, Rafael Nadal shook off dogged resistance from Nicolas Almagro to stay on course for a fifth title.

Although he maintained his record of not having dropped a set at this year's tournament, the world No 2 was made to fight all the way by his fellow Spaniard before sealing a 7-6 (7/2) 7-6 (7/3) 6-4 victory in two hours and 35 minutes.

Jurgen Melzer came from two sets down to beat No 3 seed Novak Djokovic and set up a semi-final meeting with Nadal in a marathon match.

After four hours and 15 minutes of intense battle, No. 22 seed Melzer eventually triumphed 3-6 2-6 6-2 7-6 (7-3) 6-4 as Djokovic, who has claimed to be suffering from hayfever-like symptoms, faded.

Katie O'Brien overcame a second-set stutter to see off Austria's Nikola Hofmanova 6-4 2-6 6-4 at the Aegon Trophy in Nottingham.

Compatriots Elena Baltacha and Anna Fitzpatrick also made it through to the second round as the British contingent got their grass court campaign underway ahead of Wimbledon.

Beverley's O'Brien said: "I was lucky to come through it in the third. It wasn't pretty and I think my serving and returning needs polishing up a bit before my next match.

"Sometimes it's nice to have a tough match first up as you get more time on the grass and I'll learn from my mistakes and hopefully come out better in the next round."