Croatia's Mario Ancic, the last man to beat Roger Federer on grass, stands imposingly between the champion and his 19th grand slam semi-final on Wednesday.

The 1.96 meter-tall Ancic recorded a first round victory over the Swiss world number one in 2002 to become the first teenager to win on his Centre Court debut since Bjorn Borg in 1973.

However, the 24-year-old is quick to point out times have changed now that Federer is aiming for his sixth title in a row.

"We played, I think three or four times after that. He beat me," he told reporters. "Of course it's unbelievable, because since then he hasn't lost on grass. If it was not for that, I think people would pretty much forget about that win."

Briton Andy Murray's reward for a superb comeback victory over eighth seed Richard Gasquet in the fourth round is a Centre Court showdown with second seed Rafael Nadal.

The 12th seed has not beaten Nadal in three attempts but remains upbeat about progressing to his first grand slam final.

"Obviously he's the favourite for the match. But, you know, I do think that I can win," he said.

On Court One, two highly experienced but unseeded players, Germany's Rainer Schuettler, 32, and Arnaud Clement, 30, of France are looking for a Wimbledon semi-final place for the first time.

They follow former world number one Marat Safin, who claims to dislike playing on grass, against 31st seed Feliciano Lopez. Safin, a former U.S. and Australian Open champion, and Lopez have both reached the Wimbledon quarters once before but failed to get further.