London: Novak Djokovic and Roger Federer have met 26 times, but Friday's potentially epic Wimbledon semi-final will be a first clash on grass in their rollercoaster, six-year rivalry.
Defending champion Djokovic has won the pair's last three meetings, in straight sets on clay this year in Rome and in the semi-finals of the French Open.
Those wins followed a morale-sapping semi-final 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 four of the last finals at the majors.
Federer is in a record 32nd semi-final of a Grand Slam.
On paper, the grass of Centre Court should favour 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 quarter-finals in the last two years, a crucial step for those who have written him off as past his best.
He eased past Mikhail Youzhny in straight sets in his quarter-final, 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 quarter-final.
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.
"Maybe he uses the grass court better because of his slice. He has a really smart game for this surface," said the Serb.
"But I have improved playing on grass in the last couple of years. I won the title here last year, got to another semi-final this year, so I'm feeling good about this surface, about myself on the court. I really have nothing to lose."
Friday's other semi-final sees fourth seed Andy Murray, bidding to become Britain's first finalist since Bunny Austin in 1938, and first winner since Fred Perry in 1936, taking on French fifth seed Jo-Wilfried Tsonga.
The 25-year-old Scot will be playing in a fourth successive Wimbledon semi-final, comforted slightly by knowing that Rafael Nadal, who beat him in the last four in 2010 and 2011, was knocked out in the second round.
But Murray, playing in his 10th Grand Slam semi-final, is adamant that just because the Spaniard is out, the final isn't his to take.
"When I played Roddick in the semis (2009) that was also a good chance. I had a good record against him before I played him," said Murray.
"I'm in a good position, that's for sure. Whether it's the best chance or not, I'm not sure. But I've been in this position a few times now and want to push on."
Tsonga is in the semi-finals for the second successive year, but will start as underdog having won just one of six meetings against Murray.
That came in the first round of the Australian Open in 2008 while Murray triumphed in four sets in the quarter-finals at Wimbledon two years ago.
The 27-year-old said that he doesn't envy the constant home pressure on Murray to deliver.
"I think here for Andy it's difficult because he's alone. In France it's okay. We have many players and that's fine, but here for him it's really difficult because all eyes are on him," he said.