The 27-year-old Bacsinszky broke French hearts in the other quarter-final as she beat 13th seed Kristina Mladenovic 6-4 6-4.
The first Latvian woman to reach a Grand Slam semifinal in the professional era, Ostapenko credits her strong footwork to a hobby, ballroom dancing (she prefers the samba). Both second seed Karolina Pliskova and third seed Simona Halep will compete in each respective match. Factor in that the first delay lasted over three hours and it was a day in which the mental aspect of the game was vitally important.
"At the beginning he was more a clay-court player, I would say, because we shared - his former coach is my coach now, so that's the only info I've got".
"I'm really happy, I can not believe it still", said Ostapenko.
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.
She had virtually quit the sport in 2013, exhausted of the game, and has spoken openly about how her father pushed her into tennis.
"I knew she would be a formidable opponent", the 30th seed grinned.
"I had to stay concentrated".
The women's tournament will have a first time Grand Slam champion on Saturday.
"I actually didn't expect that it would be here in Paris, but I'm really happy it's here".
Ostapenko said: "In some moments I felt a little bit tight because it was already the semi-final.
She's a big hitter", said Bacsinszky, who also lost in the 2015 French Open semifinals. Now, she has gone step further than compatriot Anastasija Sevastova at last year's US Open.
PARIS Ripping a screaming forehand straight through the tennis textbook, Latvian Jelena Ostapenko blazed into the French Open final with a 7-6 (4) 3-6 6-3 win over Swiss Timea Bacsinszky in a battle of the birthday girls on Thursday.
Timea Bacsinszky of Switzerland reacts after defeating 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.
Martina Navratilova, John McEnroe, Tracy Austin and Henri Leconte are among the greats who will also be in action this week.
And the ones with tickets for Court Suzanne Lenglen and Court Philippe Chatrier on Tuesday will get a refund as the quarter-finals did not last over two hours.
Dating back to 2007, she made the second round at Roland Garros four times, but then missed much of two years with foot and ankle injuries and came close to retiring from the sport. I think it's such a great surface. After Tuesday's victories, they ran into each other in the players' gym and hugged. Halep kept Pliskova deep in the late stages of the match, and needed only one of two match points to put Pliskova away and advance to face Ostapenko.