Even Djokovic found it hard to fathom how far he's fallen, only a year removed from leaving Roland Garros as a player nonpareil, the first man in almost a half-century to win four consecutive Grand Slam titles.
Defending champion Novak Djokovic crashed out of the French Open on Wednesday (Thursday in Manila), sparking fresh fears over his appetite for the sport he once dominated as Rafael Nadal and Andy Murray made the semifinals.
The result was all the more remarkable as in five previous matches with the 23-year-old he had lost one set and last month thrashed him 6-1 6-0 in Rome - a result that suggested Djokovic had found his mojo, missing since he won the French a year ago.
Ostapenko turned 20 on Thursday and fans on Court Philippe Chatrier sang "Happy Birthday" to her.
Were she to win the title on Saturday, Halep would take over the No. 1 ranking for the first time.
The 135-minute demolition catapulted the baseliner into elite company.
Thiem, though, excelled on the Parisian clay, breaking Djokovic in the third game of the first set. The only player to defeat Nadal in this year's clay-court season, Thiem was overwhelmed by the Spaniard in back-to-back finals at Barcelona and Madrid before returning the favour during the quarter-final of the Italian Open.
"It's going to be the toughest match you can imagine", admitted sixth seed Thiem, who trails Nadal 4-2 on head to head.
Thiem now takes on Rafa Nadal, whose quest for a 10th title continued after opponent Pablo Carreno Busta retired in the second set.
Nadal is just two match wins away from capturing an unprecedented 10th French Open.
In those later matches, No. 30 Timea Bacsinszky of Switzerland will face unseeded Jelena Ostapenko of Latvia, with both players celebrating birthdays on Thursday: Ostapenko's 20th, Bacsinszky's 28th.
Nadal has now recorded 100 best-of-five-set wins on clay from 102 matches - his only defeats coming at Roland Garros to Robin Soderling in the round of 16 in 2009, and to Djokovic in the 2015 quarter-finals. Djokovic seemed to hit a wall during the match, instead of being the rock solid obstacle like he was for the youngster at the semis a year ago.
Thiem is entering only his second Grand Slam semi-final. Federer (13 Australians, 11 Wimbledons and 10 US), Jimmy Connors (14 US and 11 Wimbledons), Andre Agassi (10 US Opens) and Djokovic (10 US Opens) are the others.
He wasted two set points in the opener.
"We tend to think Murray has less power than Nadal", he said. And it ended with Djokovic eating his first Bagel at the event.
"Thiem is a tough player".
"He's obviously played extremely well the last few years at the French, and he's confident".
Wawrinka was elated after blunting Cilic.
"I came in playing garbage", Murray said with a smile. "I was planning to play only Wimbledon".
Murray dropped the first then seized control from Nishikori in the second after a minor spat with the umpire.