By John Stonestreet

PARIS (Reuters) - The reputations of Novak Djokovic and Andy Murray as the fittest men in tennis will be rigorously tested when they slug it out on Sunday for the French Open title, at the end of a tournament in which endurance has been a prime asset.

With both men hitting peak form in emphatic semi-final wins, mental strength looks likely to decide a final given added spice by an array of historic landmarks that will fall by the wayside irrespective of who wins.

Over two weeks of often attritional tennis invariably played in damp, cold conditions and with heavy balls, Murray -- bidding to become the first British man to win in Paris since 1935 -- has put his body through close to 18 hours on court over 24 sets.

Djokovic, also seeking his first title in Paris to become the first man in almost 50 years to hold all four majors at once, has played five hours and five sets fewer.

But the rain delays that have ravaged the tournament meant the Serbian played four days in succession up to Friday and denied him the usual rest days associated with grand slams.

"When I get on the court with (Murray) it's going to be a very physical battle," Djokovic said after Friday's three-set demolition of Austrian tyro Dominic Thiem. "That's why the day off (on Saturday) will definitely serve me well."


If the pressure mounts on Sunday, Djokovic may however want to resist reflecting on his three previous defeats in French Open finals, including last year's four-set reverse against Stan Wawrinka -- a match the world number one was expected to win.

No player in the professional era has ever lost more finals at any one of the four grand slams and gone on to win that event.

And at 29, time is ticking for both of them.

"Neither of us know how many more chances we'll have to win here. It took obviously Roger (Federer) a long time to win this one (in 2009)," second seed Murray said on Friday after a superb display in beating Wawrinka.

It is in the head that Djokovic believes he may have the advantage over his Scottish opponent, a man just seven days his senior who he has beaten in four out of six major finals, and whose game he has been trying to pick apart since the first time he recalls facing him as an 11-year-old.

"It's pretty nice that our rivalry has evolved over the years," he said. "...I think mentally when we step on the court, sure, maybe to some extent, (I have) some small percentage (of advantage), but he's playing in great form."

Murray, who rated Friday's four-set win as one of his best matches on clay, is meanwhile hoping the conditions on the day may provide him with an edge.

After 12 defeats in 13 matches against the Serbian, including a loss at altitude in the final of the Madrid Open in early May, Murray turned the tables a week later in their most recent encounter, a rain-affected Italian Open final in Rome.

"(Rome) was maybe a bit more similar to here, because it was raining quite a lot of the match when we played," Murray said.

"I got off to a good start (in Rome). Novak got off to a good start in Madrid. That helped both of us in respective matches."

(Editing by Martyn Herman)