Vondrousova also reached her first major title match, eliminating No. 26 Johanna Konta of Britain.
Paris: Ash Barty came back from a set and a break down to end 17-year-old Amanda Anisimova's French Open run with a topsy-turvy 6-7 (4), 6-3, 6-3 victory Friday that put her in her first Grand Slam final.
The No. 8-seeded Barty, a 23-year-old Australian who took nearly two years off from tennis to play cricket, will face another teen for the championship Saturday: unseeded 19-year-old Marketa Vondrousova of the Czech Republic.
"I'm proud of the way I fought and found a way back into that match," Barty said. "It's just been an amazing journey that I've been on. I can't wait to see what happens tomorrow."
Vondrousova also reached her first major title match, eliminating No. 26 Johanna Konta of Britain 7-5, 7-6 (2). Vondrousova has not dropped a set in the tournament and can become the first teenager to win the French Open since Iva Majoli in 1997.
Both matches saw massive swings of momentum, particularly Barty versus Anisimova, the 51st-ranked American who hadn't ceded a set through the quarterfinals.
Barty began as well as possible, racing to a 5-0 lead within 12 minutes by winning 17 of the first 18 points.
"I felt," Barty would say afterwards, "as that happened really quickly."
Moments later, with Anisimova serving at 15-40, Barty held two sets points. From there, Anisimova began playing the way she did in her upset Thursday of defending champion Simona Halep - and Barty suddenly lost her way.
Anisimova took six consecutive games, and in the eventual tiebreaker, she collected the last five points. That began a run of 17 points in a row for her en route to a 3-0 lead in the second set. But then it was Barty's turn to change things and she went on a six-game run to force a third set.
There was one last big shift to come. Anisimova was up a break and serving at 2-1 in the third when her coach signaled from the stands that play should be halted because of rain. The chair umpire checked the white lines, though, and determined the match could continue.
Anisimova then got broken there, opening another four-game run for Barty. Even though Barty needed six match points to close things, she did, indeed, finish the job.
Vondrousova, meanwhile, trailed 5-3 in each set but came back each time. Konta wasted three set points in the opener.
The semifinals were played in difficult conditions, with drizzles that had spectators opening umbrellas, wind that reached 12 mph (20 kph) and the temperature around 60 degrees Fahrenheit (15 degrees Celsius). And they were played at unusual courts - scheduling that was criticized by women's tennis tour CEO Steve Simon as "unfair and inappropriate."
Normally, all French Open singles semifinals are held in Court Philippe Chatrier, with the women on Thursday and men on Friday. But after a full day of play was washed out by rain on Wednesday, tournament officials were forced to shuffle the schedule.
The two women's semifinals were contested simultaneously at the second- and third-biggest courts at Roland Garros instead of the main stadium, starting just after 11 a.m.
The two men's semifinals - Rafael Nadal vs. Roger Federer, and Novak Djokovic vs. Dominic Thiem - were to be played back-to-back at Chatrier.