They will face either 16th-seeded Colombian duo Juan Sebastian Cabal and Robert Farah or Ryan Harrison of the United States and Michael Venus of New Zealand.
Gabriela Dabrowski, the doubles World No.20, will play her first Slam final alongside Rohan Bopanna in the mixed doubles championship match today. Entering the tournament, Halep was a 7-2 favorite, while Pliskova was tied for the fifth-favorite, despite being the 2-seed.
Waves of weather - "We had a hurricane, a sandstorm, and we nearly had snow too", Bacsinszky said in her on-court interview - disrupted both players' games, but she said she was ready for a heavy surface.
The second-seeded Czech fended off three break points on her way to claiming the second set 6-3, clinching it with a forehand victor on her second set point.
Unseeded women are 4-15 in the French Open semifinal in the open era. Bacsinszky won 6-4, 6-4. She broke on the third time of asking in the seventh game and after saving a pair of set points on her own serve, broke when the former world #1 netted a backhand to pull back the entire deficit. As Ostapenko left the room, she turned to her agent and whispered with a wide, proud smile, "My answers are amusing".
"I practiced in Bienne a few weeks ago with (Swiss player) Victorija Golubic and it was snowing".
The world number 47 said: "I didn't expect that it would be here in Paris, but I'm really happy it's here". The other men's quarterfinals, at the end of the day, are 2016 runner-up Andy Murray vs. "It is my first semifinalist ever".
Timea Bacsinszky of Switzerland returns the ball to France's Kristina Mladenovic during their quarterfinal match of the French Open tennis tournament at the Roland Garros stadium, Tuesday, June 6, 2017 in Paris.
After seeing off Mladenovic, Bacsinszky said the weather conditions which saw heavy rain as well as 30km/h winds had been tough to deal with.
- Timea Bacsinszky after seeing off Kristina Mladenovic.
Look at the backhand victor.
Timea Bacsinszky has called a trainer on court after apparently hurting a knee while chasing a shot.
And another ferocious forehand helped her break back as Bacsinszky rallied at the start of the second. The win is impressive for Jelena Ostapenko. In 2014, back on tour, she was ranked outside the top 100 and needed to qualify for the French Open.
Ostapenko has never made the semis of a major. Ivanovic won the title at the French Open the next year. The 27-year-old, who also made the last four in 2015, overcame Mladenovic, bidding to be the first Frenchwoman in the semi-finals since Marion Bartoli in 2011, in a rain-marred game. Thiem defeated defending champion Novak Djokovic in the quarterfinals.
"I remember that I had, like, three towels that I wanted to give to my siblings because I have three", she said. Their semi-final will take place on Thursday, the same day as both of their birthdays.