Dominic blasted three winners in game six to bring the opener home in 24 minutes, producing one of the best sets against Nadal ever and hoping for more in the rest of the match!
The match, which carried on until after 2 a.m. before ending 0-6 6-4 7-5 6-7 (4-7) 7-6 (7-5), was Nadal's longest at the US Open.
Nadal said that losing the first set by 6-0 was not in his plan but he accepted it with "humility", while in the fifth he had "more options" than Thiem.
"Very demanding in all aspects", Nadal said later.
"Against Rafa, I've had three very nice experiences and seven awful experiences", said Thiem who turned 25 on Monday.
Laughing, Thiem said he did not think Nadal was "really sorry".
"(I am) sad for him because when [he arrived at] this moment, he did all the things well to win the match.
"He's young, he has plenty of time to win big tournaments, and he has everything, no?"
What was most impressive in a match that featured brilliant shot-making and powerful, line-clipping groundstrokes over the course of almost five hours was that Thiem looked to be the fresher player compared to the 17-time Grand Slam champion who is known for his fight on the court. "I don't want to lose against anybody, but now I wish him the title the most, that's for sure".
Nadal and Thiem have met ten times so far on Tour, and, remarkably, all have been contested on clay courts.
"Thank you for the all the support", he said, addressing the Arthur Ashe crowd.
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With his first words to the media, Thiem underscored the weight of this match to both men.
Naturally, Nadal was exhausted following the quarter-final win.
When it ended, on an overhead by Thiem that sailed long, everyone in Nadal's guest box - a group that included actor Ben Stiller - leaped to their feet to celebrate.
Rafael Nadal showed his class by jumping over the net to embrace Dominic Thiem. He came within two points of victory late in the fourth set before being pushed to a fifth, where he was two points from a loss.
"I'm not sorry. I'm just sorry for my legs".
Thiem - with his girlfriend and fellow tennis player Kristina Mladenovic watching from the stands where Hollywood star Ben Stiller was also present - played well, however, Nadal was just too good as he executed the third of three set points on his opponent's serve to claim the momentum.
"It's going to be stuck in my mind forever..."
"I like people who try hard to achieve their goals and he is one of them".
This was only the fourth time in 282 career Grand Slam matches that Nadal has been bagelled in a set - on the three previous occasions, he lost.
Nadal saw five break points come and go before Thiem went long with a smash on the first match point. The fourth was a wild 81-minute ride that began with Thiem facing break points, saw the Austrian threaten a double break before being pegged back and then a tired Nadal miss a chance to win the match.
Nadal holds an 11-5 record against Del Potro.