Against Ostapenko, Wozniacki only had to keep the ball in play to race to a 5-0 lead in the first set as the former found it hard to keep her eyes open.
FRENCH favourite Kristina Mladenovic skidded out of a storm-struck French Open on Tuesday, losing 6-4, 6-4 to Timea Bacsinszky in a rain-interrupted quarter-final.
Ostapenko is the first teenager to reach the Roland Garros semi-finals since Serbia's Ana Ivanovic and the first to book a place in a Grand Slam semi-final since American Madison Keys at the 2015 US Open. "Lucky her, she's way younger than I am!"
After a pair of holds were recorded to start the second set, it was the 19-year old who struck first, breaking for her first lead in the match at 2-1.
"The rain delays - one of which lasted over three hours - did Mladenovic no favours". If they both win their quarterfinals, they would meet in a semifinal showdown.
Bacsinszky will be 28; Ostapenko will turn 20. Mentally, out on the court she is such a great fighter and is really hard-hitting.
In a further numerological coincidence, she was born on the same day in 1997 that Brazil's Gustavo Kuerten won his first-ever championship in Paris.More news: Northern Irish unionists to open talks with UK's May about support
The year before that, she lost in the first round of French Open qualifying.
The Latvian teenager, ranked 47th in the world, did not wilt after dropping the first set to the 26-year-old Wozniacki, the world No. 12, who has played in two Grand Slam finals.
- Ostapenko when asked if her ballroom dancing competitions as a youngster helped prepare her for the big stage in tennis.
Bacsinszky had to deal with her own game, flying dust, Mladenovic and a volatile gallery on Court Philippe Chatrier.
Ostapenko is looking forward to her birthday showdown against Bacsinszky, adding: "We are good friends, because we played the doubles in China a year ago, and that's how I got to know her".
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.
"I have to change something compared to the last matches", Thiem, the youngest of the quarterfinalists, said.More news: '100 per cent' willing to testify over Comey conversations: Donald Trump
The world number 14 fought back the tears as she left the court, with French hopes now left to rest with Caroline Garcia, who faces world number three Karolina Pliskova on Wednesday, while Elina Svitolina of Ukraine plays Romanian number three seed Simona Halep.
The rain delays meant Rafael Nadal and Novak Djokovic will have to wait until tomorrow to contest their quarter-finals after men's play was postponed. However, she lost her serve trailing 4-5 to hand the first set to Wozniacki.
"I'm really happy, I love to be here", Ostapenko said after the crowd serenaded her with a chorus of "Happy Birthday" on the day of her 20th birthday.
Mladenovic tried to look on the positives of her French Open campaign, which at one point had been in doubt because of a back problem.
"I had to stay aggressive, and I found my game", said Ostapenko.
After play was suspended due to rain, she returned to action to cruise past Caroline Wozniacki.
"We had all the seasons - a hurricane, sandstorm and nearly snow".More news: All Blacks coach praises Lions despite slow start to tour
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