Federer on Ancic alert in quarters

The memory of a rare defeat at Wimbledon will ensure world number one Roger Federer does not underestimate Croatian Mario Ancic in their French Open quarter-final today.

Ancic was the last man to beat triple Wimbledon champion Federer on a grasscourt, winning in straight sets in the 2002 first round at the All England Club.

"I'm not going to underestimate him at all because that happened to me in Wimbledon when I lost to him," said Federer, who is trying to become only the third man to hold all four grand slam titles at the same time.

"That's the last thing I'll do. That's not going to happen. Everybody expects me to win. I know that this player is dangerous."

Ancic is playing in his first Roland Garros quarter-final and clay is not his best surface. Like, Federer, his best grand slam performances have been on grass and he reached the Wimbledon semi-finals in 2004.

The tall 22-year-old overcame cramps and vomited during his five-set fourth round win over clay specialist Tommy Robredo and Federer admitted he was impressed.

"He did an incredible job to come back in this match and to finally finish," said the Swiss.

The winner faces a tough semi-final against either third seed David Nalbandian or sixth seed Nikolay Davydenko. Both players have reached the last four at Roland Garros before but neither has yet won a grand slam.