For all that has transpired during 26 matches over seven years - 10 of them in majors - the history of Roger Federer versus Novak Djokovic has been exclusively written on hardcourts and clay. Wimbledon brings a new element to the rivalry that Federer leads 14-12, but which Djokovic has owned in recent times.
''It is our first grass court match. We don't know quite what to expect,'' six-time champion Federer admitted ahead of tonight's semi-final against Djokovic, the titleholder and top seed. ''I feel it's a bit of an even ground. You have to ask him. I feel good about the match. I'm excited.''
Djokovic said: ''I think that grass courts are suiting his style of game the most. He has a really smart game for this surface. But I improved playing on grass in last couple of years. I mean, I won the title here last year, get to another semi-final this year, so I'm feeling good about this surface, about myself on the court. We never played on grass, so I think it's going to be interesting for us to see what happens.''
Djokovic has won 32 of his past 33 grand slam matches. His only blip was the recent French Open final loss to Rafael Nadal that scuttled the glorious prospect of a non-calendar-year grand slam. But the world No.1 is aware of what Wimbledon means to Federer, of his achievements here in the past, and the records that can still be broken. ''He definitely wants to prove to himself and to everybody else that he can win it once again,'' said Djokovic.
And, one would imagine, to also demonstrate he can still beat Djokovic, his conqueror the past three times - including, bitterly, from two-sets-to-love and match points down at last year's US Open - and five times out of the last six. So what impact does such a recent head-to-head statistic have, mentally, on the player widely regarded as the finest of all?
Not much, insisted Federer's coach, Paul Annacone. ''Great players go through spells like this. Last year, Rafa couldn't beat Novak at all, and then this year now he has been able to,'' Annacone said.
''Great players adjust and adapt and they know what to expect from other great players. And the margins are so narrow with these guys, it's so close. Roger had a couple of match points in a couple of those matches, and I just think if there's a landslide or you're just a regular pro player without a championship pedigree, then it makes it a little bit more difficult. But I think he's pretty comfortable.''
It will be far different, of course, than his quarter-final against his tasty bunny Mikhail Youzhny, a slaughter witnessed by tennis sovereigns Andre Agassi and Steffi Graf, and local royalty the Duke and Duchess of Cambridge. So majestically did Federer rise to the occasion that Youzhny was prompted to ask Agassi, seated in the front row ''what I have to do?'' to interrupt the rout that was his 14th consecutive loss to the former king.
Agassi just laughed, as did Youzhny, and the exchange also amused Federer - clearly thrilled with his best form of the tournament and also satisfied there was no reprise of his previous-round back troubles as he prepared for a match that will be far more testing, against an opponent who claims to be feeling as confident as when he won the title last year.
So what difference will grass make? ''I don't think a whole heck of a lot,'' said Annacone. ''There's no secrets out there between the players, especially when they get to this stage of the tournament. Grass isn't the way grass used to be, but Roger's won here so much that he's pretty comfortable on it.''