Romanian and world number one Simona Halep broke Spaniard Garbine Muguruza's serve six times in a ruthless display to set up Saturday's final against US Open champion Sloane Stephens.

Romania's Simona Halep celebrates winning her semifinal match against Spain's Garbine Muguruza, Paris, France, June 7, 2018.
Romania's Simona Halep celebrates winning her semifinal match against Spain's Garbine Muguruza, Paris, France, June 7, 2018. (Reuters)

World number one Simona Halep will have another opportunity to claim her first Grand Slam title after beating Spain's Garbine Muguruza 6-1 6-4 in their French Open semifinal on Thursday.

The Romanian broke Muguruza's serve six times in a ruthless display to set up Saturday's final against US Open champion Sloane Stephens.

Halep has suffered defeat in her three previous Grand Slam final appearances, including two in Paris in 2014 and 2017.

"I'm happy to play the final again at my favourite grand slam," Halep said courtside. "I'll try my best and hopefully do better than last year."

Muguruza, the 2016 champion, set about attacking Halep from the start but whereas all her previous opponents this fortnight has withered under the onslaught, battle-hardened Halep barely took a backward step.

Hurling everything Muguruza fired her way back across the net with equal venom Halep made a lightning start and was 5-0 up despite her opponent not playing badly herself.

The tall Muguruza had not dropped a set before facing Halep and thrashed two Grand Slam champions in Sam Stosur and Maria Sharapova for the loss of five games en route to the last four.

The 2016 French champion and reigning Wimbledon champion ratcheted up the intensity in the second set and broke in the third game when a powerful return forced an error.

Halep weathered the storm and broke back for 4-4 before winning a marathon ninth game in which she saved three break points to pile the pressure on the third seed.

Halep seized her chance, moving 0-40 ahead and then raising her arms in triumph as Muguruza blazed a backhand long – her 31st unforced error of the match.

"I knew that I have to be aggressive like her. I knew that she's gonna start the match with a lot of power," Halep, one of the best tacticians on the circuit, told reporters.

Sloane Stephens of the US in action during her semifinal match against Madison Keys, Paris, France, June 7, 2018.
Sloane Stephens of the US in action during her semifinal match against Madison Keys, Paris, France, June 7, 2018. (Reuters)

Stephens tops Keys

Stephens maintained her spotless record against fellow American Madison Keys with a 6-4 6-4 win in the day's other semifinal clash.

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.

Stephens had previously never gone past the fourth round in Paris.

Regardless of the result on Saturday, the 25-year-old Stephens will become the first American other than the Williams sisters 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. Merci Paris, je t'aime.

Spain's Rafael Nadal in action during his quarterfinal match against Argentina's Diego Schwartzman, Paris, France, June 7, 2018.
Spain's Rafael Nadal in action during his quarterfinal match against Argentina's Diego Schwartzman, Paris, France, June 7, 2018. (Reuters)

Nadal advances to semis

Men's defending champion Rafael Nadal dropped his first set at Roland Garros since 2015 but recovered well to beat Argentine Diego Schwartzman 4-6 6-3 6-2 6-2 in a rain-delayed quarterfinal clash.

The world number one was a set and a break down on Wednesday before he regrouped and blazed through the last two sets on Thursday in a last-eight showdown which was played over two days due to rain.

"I am a human person," the Spaniard, who next faces Argentine Juan Martin del Potro, told reporters following his 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.

"The quarterfinal was an important match for me. Was a match that maybe is a key match," the 16-times Grand Slam champion said.

"Even if it was 6-3 6-4, it was an uncomfortable match for me. I knew it was going to be a tough match and I was a little bit more nervous than usual. That's why."

The Spaniard, bidding for an 11th title at Roland Garros, will meet fifth seed Juan Martin del Potro in Friday's semifinal after the Argentine overcame Marin Cilic 7-6(5) 5-7 6-3 7-5.

Argentina's Juan Martin Del Potro serves to Croatia's Marin Cilic during their quarterfinal match of the French Open tennis tournament, Paris, France, June 7, 2018.
Argentina's Juan Martin Del Potro serves to Croatia's Marin Cilic during their quarterfinal match of the French Open tennis tournament, Paris, France, June 7, 2018. (AP)

Del Potro looking to blunt Nadal's domination at Roland Garros

Del Potro has looked one of the biggest threats to Nadal's domination this year, with his pulverising forehand dismantling everyone in his path on the Parisian clay.

After dropping the opening set of his first round match he won the next twelve. Cilic, who like Del Potro stands 1.98 metres tall (6 feet 6 inches), owns a US Open title, has a beast of a serve and always looked like being his first serious test. And so it proved.

After returning to a sunny Court Suzanne Lenglen locked at 5-5 in the first set tiebreak after battle was halted because of rain on Wednesday, DelPotro flirted with danger before racking up an eighth win in succession against Cilic.

He appeared almost overcome with emotion after reaching his first French Open semi-final since 2009, when he was beaten by eventual champion Roger Federer.

"Well, it's tough to speak," the 29-year-old, who has risen back to sixth in the rankings after battling back from three left wrist surgeries, said on court as fans sang "Delpo, Delpo".

Asked about facing Nadal, who he has beaten five out of 14 times but never on clay, he was drowned out by his fans who clearly believe in their man's chances.

"It's a challenge that every player wants to have," he said. "I don't know if I will win, but I will take big love from you and that's most important for me."

The first set always looked key and Del Potro clinched the opener as Cilic blinked first.

Mixed doubles

Taiwan's Latisha Chan and Croatian Ivan Dodig beat Australian Open winners Gabriela Dabrowski and Mate Pavic 6-1 6-7(5) 10-8 to win the mixed doubles title.