That the pair have only ever met on clay is remarkable, and few players have had as much success against Nadal on that surface, even if the Spaniard has the superior head-to-head record.
World No.1 Rafael Nadal will play Argentine Juan Martin del Potro in his 11th French Open semi-final appearance, while Simona Halep has reached her third final and held on to her world No.1 spot with victory over Garbine Muguruza. He beat me in Madrid and he has incredible power.
"If I want to beat him, I have to play that way like I did in Rome and in Madrid. Del Potro hasn't played Nadal enough on clay to feel the scar tissue, to feel the damage that Nadal has done on so many players so therefore I understand why Juan Martin would choose to not risk it and play safe", he explained. I believe I can be ready for that final. However, after the game, Nadal revealed that he was struggling against Del Potro in the first set.
This was the No. 5-seeded del Potro's first semifinal at Roland Garros since 2009.
"Nadal, in Paris, best-of-five, is still half a class above Dominic, half a level too good", said Bresnik, who has coached Thiem since Thiem was 9.
The first semi-final was between Thiem and surprise semifinalist, Marco Cecchinato, and it was a hard fought match with the first two sets setting the court alight.
The toughest task yet is yet to come though, when he will face someone who had reached the final at Roland Garros 10 times before and never lost.
Nadal might not be able to get away with a nervy start against an opponent like Thiem, who is the only player to defeat him on clay in the build-up to Roland Garros over the past two seasons.
"I am in a positive way always on court", Nadal said.
"I think the big key was the second set because it was a close tie-break", said the 24-year-old.
"I think for me it is very important today, because I playing against Dominic". Looking at just 2018 tour, however, Nadal is just 1-1 against his younger opponent. However, I'm going to be aggressive and have a small bet on Thiem winning 3-0, now available at around [20.00].
"He's too strong. He's improving his backhand a lot".
But Thiem, unusually standing up to Nadal's first serve, forced two break points in the next game and converted the second with a flashing forehand into the right corner. The Austrian looked very assured against Alexander Zverev as well as Cecchinato.
Rattled by the Italian's revival, Thiem clicked into overdrive - and aided by Cecchinato unforced errors - clinched a crucial break for 6-5 by crunching a forehand victor.
The first set had taken 57 minutes, in stiflingly humid conditions, but there was to be no let-up for the underdog in the second.
The pivotal part of the match was the second-set tiebreaker.
He does see new maturity in Thiem, more controlled aggression on critical points and more skill on the attack. He gave Nadal a sound beating in Madrid, and whilst that has never been Nadal's favourite tournament - with suggestions that the relative altitude makes the ball travel faster through the air, dulling Nadal's usual advantages on clay - I'm inclined to view it as a sign of a growing equality on clay between the two of them.