PARIS, France - The Final Four is set for Thursday at the French Open. And after all the talk of an open field at Roland Garros this year, the semifinals will be helmed by four familiar faces. 

First up, No.1 Simona Halep and No.3 Garbiñe Muguruza are will face-off in the semifinals at Roland Garros and the match will determine who will be ranked No.1 after the Parisian fortnight. Following them will be an All-American battle and rematch of the 2017 US Open final, where No.10 Sloane Stephens is looking to upend No.13 Madison Keys to make her second Slam final in the last 10 months and crack the Top 5 after the tournament.

Play begins at 3pm local time on Court Philippe Chatrier. 

Since the start of her 2016 French Open campaign, Muguruza is 27-0 at the Slams when winning over 70% of her first serve points. (Getty Images)

No.1 Simona Halep vs. No.3 Garbiñe Muguruza (Muguruza leads the head-to-head 3-1). 

'Grand Slam Garbi' has looked in dominant form in Paris. The 2016 Roland Garros champion and reigning Wimbledon champion has not dropped a set heading into the semifinals, and she put an exclamation point on her run so far in the quarterfinals, where she lost just three games to two-time champion Maria Sharapova. 

Muguruza came into the tournament without much lead-in form, having gone 2-3 record over the clay-court season. But this is nothing new for Muguruza. She has won 6 titles in her career, yet two of them have been major titles. Last year she went into Wimbledon with a 3-2 record on grass and walked away with the title. 

The youngest active multiple-major champion has quickly proven that she knows how to play the Slams. Since the start of her title run at Roland Garros in 2016, the 24-year-old has posted a 32-6 (.842) record at the Slams. By contrast, she is 55-35 (.611) outside of the majors. 

"I don't feel I'm favorite for this match, because she's played better than I have this year," Muguruza said. "She loves clay. She loves Roland Garros. She's shown it. 

"It's a great match. It's a great semifinals. I'm motivated, and that's it. That's all."

We can argue until the cows come home as to the favorite tag, but Muguruza has looked incredibly impressive. She has served very well through her four full matches (she advanced in the quarterfinals due to a retirement). She is winning 72% of her first serve points over the tournament and 54% of her second serve points as well. She has been broken 6 times but has broken serve 22 times. 

Simona Halep has made the quarterfinals or better at her last nine clay events. (Getty Images)

As she looks to make her third Roland Garros final and second consecutive major final of the season, No.1 Halep cannot afford the slow starts that have been the only spots on an otherwise spotless tournament. The Romanian rallied from 0-5 down in the first set to defeat Alison Riske in the first round. She came back again from 0-4 down in the first set to defeat Angelique Kerber 6-7(2), 6-3, 6-2 in the quarterfinals. After match point went her well against the German, Halep turned to her box and pointed to her head. Mentally, she's a different player these days.

"It was really about the mental," Halep said. "And also physical, for sure, but mentally I was strong.

"After losing that [first] set, when I came back, it was a little bit tough, but I stayed there. I stayed focused. I never gave up. So I think that's why I won today. My head won it."

Halep has been returning very well in Paris. Her serve has been broken 12 times but she has broken 32 times. This match will feature the two best returners left in the tournament, with Halep breaking 63% of the time and Muguruza breaking 61% of the time. 

The No.1 ranking was also on the line the last time these two faced off. That last summer in the Cincinnati final. Muguruza lost just one game. Muguruza's three wins over the Romanian came on hard court. Halep's sole win came on clay in 2015. 

"She's playing fast with everyone. So doesn't matter who is playing against. She does her game. So I have just to stay strong, to try to make her uncomfortable on court, and to try to play my game.

"She's a great player. She was in this position. She won this tournament. So tomorrow is going to be a big challenge for me."

"I have no pressure," Halep said. "I played well this tournament. Every match was better and better. I had tough opponents. Tomorrow I face another one.

"So I have also no expectations, no pressure. I just want to play as I did today, and as I did every day. If I do that, I will be okay after the match, no matter the result."

Sloane Stephens will rise to No.4 if she advances to her second Slam final in 10 months on Thursday. (Getty Images)

No.10 Sloane Stephens vs. No.13 Madison Keys (Stephens leads the head-to-head 2-0).

If 'Grand Slam Garbi' is a thing, 'Slammin' Sloane Stephens' might be another. The reigning US Open champion has found her form once again, and this time she goes into a Slam semifinal as the favorite. The 25-year-old was made to battle in her third round match against Camila Giorgi, where the Italian served for the match twice but Stephens ultimately prevailed 8-6 in the third. Since then she has notched dominant wins over two of the most impressive clay-courters of the season in Anett Kontaveit (6-2, 6-0) and Daria Kasatkina (6-3, 6-1). 

Fitter and stronger than she was 10 months ago in New York, Stephens has been posting dominant numbers in Paris. She has won nearly 70% of her second serve points, while crushing her opponent's second serves, winning 70% of her return points on second serves. Stephens' serve has been broken just six times over the fortnight, while she's broken 27 times. In 8 of the 11 sets she's played, she's lost fewer than three games in a set. 

"I'm playing well, in a good space," Stephens said. "I like clay. I mean, the court suits my game pretty well. Like I said, you have to just take your opportunities when you get them, and it's just match by match, basically."

Madison Keys has made two Slam semifinals in her last three Slam appearances. (Getty Images)

Stephens' break-rate will be tested against her good friend Keys in the semifinal. Stephens has yet to face a serve like Keys' in this tournament, and Keys has yet to drop a set as she's navigated her way into her first French Open semifinal.

But Stephens has yet to lose a set to Keys in their two previous meetings and Keys has come through a very open quarter of the draw that was supposed to be anchored by No.4 Elina Svitolina. The highest-ranked opponent Keys has faced over the fortnight was No.20 Naomi Osaka in the third round. And the last time they faced off, Stephens won 6-3, 6-0 over her rattled younger opponent to win the US Open. 

"Honestly, the Open feels like it was 12 years ago at this point," Keys said. "I obviously rely on what I learned there and how to manage my emotions and manage the moment, but there were so many late nights and I was so tired. It feels completely different here."

Keys leads the semifinalists in 1st serve points won over the tournament, 77%, but ranks last in 2nd serve points won with 51%. Protecting her service games against Stephens will require a very good 1st serve percentage to minimize the number of looks Stephens gets on the second serve. Off the baseline, Stephens will bait Keys to go for too much, using her speed and counter-punching ability to shrink the court. With heavy conditions expected on Thursday, Keys should have the extra to set up her big forehand. The question is whether the shot will be there when she needs it. 

"I think for me it's been being smart about it," Keys said. It's still going for my shots, because that's how I play my best tennis. And it's trusting that my shots are going to be there when I need them in the big moments.

"But it's also not being dumb," she said with a laugh. "It's being smart about it and waiting for the right ball."

Both Keys and Stephens completed their Grand Slam quarterfinal set in Paris this year and Keys has now made the semifinals or better at 3 of the 4 majors. Ironically, perhaps, the only one missing is the Slam everyone expects her to someday win: Wimbledon. That she's into her first Slam semifinal on Roland Garros' red clay may seem a surprise to many, but Keys has had European clay success before. She defeated Garbiñe Muguruza en route to the 2015 Rome final, where she lost to Serena Williams. With Keys' weapons, she can win anywhere, anytime, any day. Her semifinal clash with Stephens will be the ultimate test of her nerves and her patience. 

"I have actually been told quite often that I'll never win or do well because I'm too nice of a person and I just don't have it," Keys said. "I think that's a load of crap, but, you know, it's just me.

"I don't think you have to be mean in order to win matches. I think there's a difference between being intense and wanting it and fighting and just not being nice, so that's something that I have always stayed true to. I'm not ever going to try to be a person that isn't nice, so that feels more authentic to me and I think I'm still doing okay while trying to be as nice as possible."

Stephens said it's all gossip and ice cream when the two are off the court, but everything gets checked at the door when it's time to battle it out. 

"You have to go out there and compete just like you do every single match," Stephens said. "Doesn't matter who is across the net.

"But I think off the court, when we're not playing, we're fine. But when we get on the court, it's go time and it's time to compete and you have to put everything else aside, and you have to compete at your best."