Novak Djokovic insists the primal screams he unleashed on beating Matteo Berrettini at the French Open were just his way of "liberating the tension" that had been building up inside him like a pressure cooker.

To Rafael Nadal, though, they can only have sounded like a guttural war cry.

For it is obvious the world No.1 is after him, with a manic look in his eyes and utterly focused on achieving what he believes must be the most difficult feat in tennis - becoming the only man ever to beat Nadal twice in his Court Philippe Chatrier kingdom.

Robin Soderling famously knocked out Nadal in 2009, while Djokovic's only victory over the Spaniard at Roland Garros came six years ago in the quarter-finals.

"And that's it, actually," the Serb reminded reporters with a smile this week.

Just two Nadal conquerors in 107 matches stretching back over 16 years. Quite, quite unreal.

"It's not like any other match," Djokovic mused, pondering the prospect of a 58th edition of one of sport's great rivalries in Friday's semi-finals.

"Let's face it, it's the biggest challenge that you can have playing on clay against Nadal on this court in which he has had so much success," said the Serb.

"In the final stages of a grand slam, it doesn't get bigger than that.

"When we face each other, there's that extra tension and expectations. Just vibes are different walking on the court with him.

"But that's why our rivalry has been historic for this sport.

"I'll probably pick Rafa as the biggest rival I've ever had in my career."

It inspires the world No.1 that Nadal stands there on the clay almost like the peak he has never been properly able to conquer.

For though the overall head-to-head reads Djokovic 29 Nadal 28, it is 7-1 to Nadal at the French Open and an overwhelming 19-7 to the Spaniard in all clay-court duels.

Djokovic still has not got last year's drubbing in the Roland Garros final out of his mind either.

"He just dominated," said the Serb, remembering the humiliation of being fed a 'bagel' set and managing to only win seven games in a 6-0 6-2 7-5 defeat.

But that heavy October Sunday is ancient history, he believes.

"The quality and the level of tennis that I've been playing in the last few weeks on clay - Rome, Belgrade and here - is giving me good sensations and feelings. I'm confident," Djokovic said.

"I believe I can win."

Yet even in their last encounter in the Italian Open final, Nadal found a way to triumph in three sets.

And, in truth, not even some extraordinary resistance from little Diego Schwartzman to take a set off the champion suggested more than a smidgen of vulnerability in Nadal as he seeks that record-breaking 21st slam.

It says everything about the pair's rivalry that not even a mouth-watering duel between the brilliant young pretenders Stefanos Tsitsipas and Alexander Zverev in the first semi can take away top billing.

Tsistipas has been playing at a level where even an analyst of Boris Becker's stature shrugs that he cannot see any weaknesses, and his 5-2 career record over Zverev demands the Greek is seen as favourite.

"But my ego tells me I want more," says Tsitsipas, eyeing his first final in his fourth semi.

Yet with a couple of miraculous old warriors waiting, that ego could still yet take a serious dent.