World No.1 Rafael Nadal will play Argentine Juan Martin del Potro in his 11th French Open semi-final appearance, while Simona Halep has reached her third final and held on to her world No.1 spot with victory over Garbine Muguruza.

Clay court supremo Nadal and 10-time French Open champion Nadal admitted to bout of nerves during his hard=fought quarter-final win over Argentinian underdog Diego Schwartzman.

The Spaniard was a set and a break down on Thursday morning before he regrouped and blazed through the last two sets on Friday morning (AEST) in a last-eight showdown played over two days due to rain.

“I am a human person,” Nadal said following his 4-6 6-3 6-2 6-2 victory.

“Sometimes you play better, sometimes you are more nervous.”

The 11th-seeded Schwartzman appeared to have done his homework well as he dominated the early exchanges to bag the opening set: an achievement in itself as it was the first one Nadal had lost at Roland Garros since 2015.

“Even if it was 6-3 6-4, it was an uncomfortable match for me,” Nadal said.

“I knew it was going to be a tough match and I was a little bit more nervous than usual. That’s why.”

Friday will be the second time Nadal and Del Potro meet at Roland Garros. Their previous match up saw the Spaniard beat del Potro in straight sets in the opening round in 2007.

The winner will play either seventh seed Dominic Thiem, who appears in his third straight semi-final in Paris or Italian Marco Cecchinato, who will hope to continue his dream run having beaten former champion Novak Djokovic in the last round.

In the women’s draw, Halep is yet to win a grand slam title but looks ominously ready to break her duck at Roland Garros when she faces Sloane Stephens in the decider on Saturday.

Simona Halep celebrates her victory against Garbine Muguruza. Photo: Getty

Muguruza had hammered Maria Sharapova in the quarter-final but Halep was a different proposition entirely – and it seemed she knew it. A nervous start from Muguruza was immediately pounced upon by Halep for a break in the opening game.

Half an hour later 1-0 had become 6-1 and the challenge of Muguruza, who would have taken over at the top of the rankings with victory, appeared to be fading fast.

She improved in the second set, breaking early on only to be pegged back at 4-4 before Halep held a marathon ninth game and broke for a 6-1 6-4 win.

“I’m really, really happy that I won this match,” said Halep, who lost to Jelena Ostapenko in the final last year.

“It was really important for my mind to know I could win against a great opponent.

“It’s a pleasure to play here. I’m happy to play the final again at my favourite grand slam. I’ll try my best and hopefully do better than last year.”

Halep will face Stephens after the US Open winner maintained her perfect record against fellow American Madison Keys with a 6-4 6-4 win in the other semi-final.

In the first all-American Roland Garros semi-final since 2002, the 10th-seeded Stephens stayed composed throughout as Keys, who has not won a set against her in three meetings, peppered the court with unforced errors.

Regardless of result against Halep, the 25-year-old Stephens will become the first American to break into the top five in the WTA rankings since Lindsay Davenport – Keys’s coach – in 2006.

“It’s always hard to play someone from your country and such a good friend, but I’m happy I played my tennis,” Stephens said.

“This is one of my favourite tournaments and I’m looking forward to Saturday.”

-with AAP