Defending champion Iga Swiatek was pushed hard by Beatriz Haddad Maia at the French Open on Thursday, but the top seed soaked up the pressure to overcome the Brazilian 6-2, 7-6(7) and reach a third final in four years at Roland Garros.
She will play on Saturday the unseeded Karolina Muchova, who saved a match point before overcoming second seed Aryna Sabalenka 7-6(5), 6-7(5), 7-5 to end the Belarusian's hopes of becoming world number one.
Swiatek, who lifted the Suzanne Lenglen Cup last year and in 2020, was put through the wringer by Haddad Maia but held her nerve in a tense tiebreak to see off the 14th seed's challenge.
"She has a really nice game for clay courts with a lot of top spin," Swiatek said of Haddad Maia, who beat the Pole in their only other meeting in Toronto last year.
"She can also play flat and aggressive. She's a fighter. For every match, she played fierce."
Sabalenka would have taken over top spot in the rankings by winning the title in Paris, but the Australian Open champion wasted her opportunity at 5-2 in the third set against Muchova and bowed out after losing the last five games in a row.
That made Muchova only the third player ranked outside the top 40 to reach the Roland Garros final after Jelena Ostapenko (2017) and Swiatek (2020) - both of whom won the title.
The last unseeded player left in the men's and women's draw, Muchova, who fought back from the mid-200s into the top 50 after an injury in 2021, was at her skilful best to subdue the big-hitting Sabalenka.
"I don't really know what happened," Muchova said. "The atmosphere, the people pushing me in all the match. I just keep fighting and it worked. I really don't know what happened. I am so happy."
There was light at the end of the tunnel for Japan's Miyu Kato after a difficult few days, as she put her women's doubles disqualification behind her to claim the mixed doubles crown with Germany's Tim Puetz.
The pair rallied to beat Canada's Bianca Andreescu and New Zealander Michael Venus 4-6, 6-4 (10-6) in the final.
Kato and her Indonesian partner Aldila Sutjiadi had been disqualified from the women's doubles in the third round when Kato hit a ball down the court between points, inadvertently striking a ball girl. That led to the Asian pair's disqualification, leaving Kato in tears.
"It's been challenging mentally after the disqualification. I want to thank everyone for the heartfelt messages of support," Kato said.
"I was able to use all the positive energy so I could be here today. Thanks to Aldila and all the Indonesian fans. I'm doing my best so we can one day return and claim the women's doubles title."
The action resumes on Friday with the men's semi-finals, as world number one Carlos Alcaraz meets 22-times Grand Slam champion Novak Djokovic and last year's runner-up Casper Ruud faces Alexander Zverev.