MADRID (AFP) - Novak Djokovic will play Stefanos Tsitsipas for the Madrid Open title after the 20-year-old Greek stunned Rafael Nadal on Saturday (May 11) to win a thrilling semi-final 6-4, 2-6, 6-3 on his fourth match point.

Nadal had been a clear favourite to face world No. 1 Djokovic in Sunday's showpiece at Caja Magica but the 17-time Grand Slam champion extended his stuttering build-up to the French Open with another surprise defeat.

Tsitsipas' victory means he reaches his fourth ATP final of the season while vindicating those that have him circled as a future star of the game.

"Emotionally it was very tough, it was one of my toughest wins," Tsitsipas said.

It might be too early to expect the world No. 9 to challenge at Roland Garros later this month but, with a fearless style and formidable forehand, he is developing a habit for delivering on the big stage.

He ousted Roger Federer from the Australian Open in January and, as well as Nadal, has beaten Alexander Zverev and Dominic Thiem, both twice, and Djokovic, whom he played on hard court in Canada last year and prevailed in three sets.

Tsitsipas will draw confidence from that result ahead of the final but arguably even more so from overcoming Nadal, on clay, which Djokovic had earlier described as the "ultimate challenge" following his own 7-6, 7-6 victory over Dominic Thiem.

By his own high standards, Nadal's clay-court swing has been disappointing.

He lost in the last four in both Monte Carlo and Barcelona, arriving in Madrid without winning either tournament for the first time since 2015.

"I have not played well enough," admitted Nadal. "I've won a lot for many years on this surface but this year it hasn't been like that."

Few would bet against the Spaniard claiming a 12th success in Paris but the showings of Djokovic, and Thiem, in this tournament suggests it is far from a foregone conclusion.

Nadal seemed to have the momentum after winning 13 out of 16 points at the end of the second set but he spurned two break points in the decider before Tsitsipas broke twice for 5-2.

Still Nadal fought back, breaking back once and then saving three match points, the last after a nerve-shredding drop-shot.

But a missed volley followed and, at the fourth time of asking, a relieved Tsitsipas finally got over the line when a weary Nadal backhand hit the net.