Novak Djokovic and Roger Federer have met 26 times, but Friday's potentially epic Wimbledon semifinal will be a first clash on grass in their rollercoaster, six-year rivalry.

Defending champion Djokovic has won the pair's past three meetings, in straight sets on clay this year in Rome and in the semifinals of the French Open. Those wins followed a morale-sapping semifinal loss for Federer at the US Open where the Serb, for the second successive year, saved match points before driving another dagger into the great Swiss.

Both men go into Friday's clash having racked up impressive numbers.

Djokovic, the US Open, Australian Open and Wimbledon champion, is in a ninth successive Grand Slam semi-final and has played in the past four finals at the majors.

Federer is in a record 32nd semifinal of a Grand Slam.

On paper, the grass of Centre Court should favor Federer, the six-time champion desperate to equal the record seven set by Pete Sampras.

But the 16-time Grand Slam title winner is playing down the significance of the surface.

"Things are not that drastic of a change anymore from clay, hard court, indoor, to grass. But it is interesting that this is our first grass-court match," said Federer.

"I'm just happy that I'm around further than I've been the last couple of years. So it's been a good tournament for me. It gives me confidence going into a big match against Novak."

Federer has enjoyed the morale boost of getting to the last four having lost in the quarterfinals in the last two years, a crucial step for those who have written him off as beyond his best.

He eased past Mikhail Youzhny in straight sets in his quarterfinal, showing no signs of the back pain that dogged him in the previous round or the struggles of the third round when he was two sets to love down before beating Julien Benneteau.

But top seed Djokovic has been untroubled, dropping just one set en route to the last four, a run capped by a comfortable straight sets win over Florian Mayer in his quarterfinal.

Djokovic said he will be wary of the dangers posed by Federer on the Wimbledon grass where the Swiss star's record now stands at 64 wins against just seven losses in his 14 visits.

Agence France-Presse