Novak Djokovic's grand slam winning streak is over.
Thiem's 6-2 3-6 7-5 5-7 7-5 victory ended the world No. 1's unblemished 26-match run in majors that began last year at Wimbledon.
It also quashed his hopes of landing four straight grand slams for the second time.
Thiem, meanwhile, will be the one facing Rafael Nadal in the final for a second straight season. He became the first player outside the big three of Nadal, Djokovic and Roger Federer to make back-to-back men's finals at Roland Garros since Sweden's Robin Soderling in 2009 and 2010.
Thiem's task was always going to be difficult versus the 11-time champion -- Nadal won in straight sets in 2018 -- but even more so now given the draining win over Djokovic and no day off between the semifinal and final.
The fourth seed spent almost three hours on court Saturday after proceedings were paused with the 25-year-old ahead 3-1 in the third Friday.
"I'm feeling fine," said Thiem. "I'm full of adrenaline, of course, still from today's match and also I will have that tomorrow. I'm not going to be tired. It's all going to come after the tournament.
"So I'm ready to leave all or everything that I have left out on the court tomorrow."
Twelve months ago at the French Open Djokovic left in deep frustration, too, losing to the relatively unknown Marco Cecchinato in a quarterfinal where he had chance after chance.
Djokovic clashes with umpire
In still blustery conditions in Paris -- though not nearly as windy as Friday -- Djokovic became agitated when chair umpire Jaume Campistol handed him a time violation warning while serving at 5-6, 30-15 in the third set. Djokovic has been known, like Nadal, to take his time between points on serve.
He later appeared to tell Campistol to wait for the crowd to settle before starting his shot clock.
Soon after Thiem ripped a backhand return on a fourth set point, the 15-time major champion received a warning for unsportsmanlike conduct. His frustration grew.
Djokovic asked Campistol, "Have you ever played tennis?"
Campistol replied "yes."
"So you know how it is in this situation at 5-6, long point, crowd still clapping, right?"
"You've made yourself recognizable now," he also said.
It ultimately was that kind of semifinal for Djokovic.
"Obviously when you're playing in hurricane kind of conditions, it's hard to perform your best," Djokovic told reporters moments after stepping off court.
"It's really just kind of surviving in these kind of conditions and trying to hold your serve and play one ball more than your opponent in the court.
"That's what it felt like playing yesterday."
Due to the extreme wind, Djokovic asked supervisor Andreas Egli to stop the contest in the first set. He was rebuffed.
"He said as long as there are no flying objects coming to the court, we're good," said Djokovic. "I didn't know that an umbrella is not a flying object, which flew in in the first game of the match, but that's their decision. I guess they know tennis better."
After a second rain delay, organizers suspended play at 6:30 pm local time despite the rain stopping and the sun making an appearance.
Some suggested Djokovic left the grounds before the tournament officially made the decision but he said that wasn't the case.
"I left when they canceled the match for the day," he said.
Asked why the postponement came, Djokovic replied: "I don't know. You can ask them."
Upon the restart, Djokovic constantly pressured Thiem and got his reward to pull to 3-4 in the third.
At 4-4 on another break chance, a 21-shot rally concluded with the Austrian hitting a drop shot winner -- off the net.
The drama of the extended 12th game ensued, a game in which Thiem sent a routine backhand slice long on a first set point. A first serve into the body plus an ace fended off two more set points prior to Thiem anticipating Djokovic serving and volleying and crushing a backhand.
Djokovic grabbed an early break lead in the fourth but Thiem leveled and even led 5-4.
One game from victory and at 0-15 on the Djokovic serve, Thiem error's helped a relieved Djokovic hang on.
As the tension escalated, Djokovic broke in the next game courtesy of a double fault.
There were extended, breathtaking rallies, including when the speedy Thiem conjured another break chance by racing to a drop shot and deftly putting his angled, backhand reply past Djokovic.
Djokovic held firm but then erred on a break point at 1-1 in the fifth. And what a chance it was.
As the drop shots accumulated, Djokovic comfortably got to one of Thiem's but pushed his forehand long.
It clearly took a toll, as this time Djokovic buckled in the next game when his volley clipped the tape and dropped on his side.
You could say the net was rooting for Thiem, given that at another stage one of the Austrian's passing shots struck the tape and turned into a lob over the stranded Djokovic.
Djokovic saved a break point at 1-4, with the rain once again intervening to stop play.
Dramatic last set
Incredibly the first point after the hour delay -- which cut into the women's final due to start at 3 pm local time between Ashleigh Barty and Marketa Vondrousova -- saw Djokovic and Campistol disagreeing about a ball mark when the Serb stopped playing off a Thiem ball near the baseline.
The point thus going to Thiem, Djokovic saved the second break point with a good serve then broke for 3-4.
With all the momentum Djokovic, however, stuttered -- crumbling from 30-0 to trail 5-3.
The drama, though, didn't end there.
Seemingly cruising to victory at 40-15, Thiem missed a pair of backhand slices -- one into the net and one wide -- on two match points.
On break point, he snatched at his backhand and sent it into the net.
But Djokovic couldn't save a third match point at 5-6, as Thiem blasted a forehand winner to book a clash with Nadal.
"Somehow I had the feeling that I had the lead in the whole match, and then at the end it got so tough," said Thiem. "At the end, both of us could win, and I luckily got" the win.
Thiem improved to 2-1 against Djokovic at the French Open but hasn't taken a set off Nadal in their three Paris tussles.
And unluckily for Thiem, Nadal is playing his best tennis of the current clay swing.
"I try to keep all the positive emotions I'm having right now from this amazing match today," said Thiem. "And go with a really positive mind into the match tomorrow.
"Then we'll see."
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