If there were any reason for a bit of intrigue entering Sunday, it was this: Thiem beat Nadal on red clay at Rome in May 2017 and again at Madrid last month.
Only two players have managed to beat Nadal at the French Open since he first bounded into Roland Garros in 2005 armed with a bulging left bicep, pirate trousers and a pulverising brand of claycourt tennis the like of which had not been seen before.
"I saved two set points and luckily I won it".
Nadal has dropped only one set in the ongoing tournament but he was tested by del Potro's compatriot and 11th seed Diego Schwartzman in a rain-interrupted quarter-final tie.
Thiem's fighting spirit was evident in abundance - he continued to put pressure on Nadal through his return game, while consistently scrapping to stave off perilous positions on his own serve - but ultimately the Spaniard's quality and, often, his sheer force of will, won the day.
Rafael Nadal powered his way into the French Open final and then claimed he can still move up another gear.
"The second set tie-break was the big key to the match, 100 per cent, because obviously he felt all the matches from the past two weeks after that", said Thiem, according to ATP's website. That began a run of four consecutive French Open triumphs through 2008.
"True, I understand that everybody here, you have to write things", he said.
Only three times (once when he withdrew with an injury) has the Mallorcan not reached the French Open final since he first re-defined claycourt tennis in 2005 as a sleeveless warrior.
While Thiem beat Marco Cecchinato in first semi-final to reach his first Grand Slam final.
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There was a sense of inevitability when Del Potro served at 4-5 and Nadal turned the screws to grab two set points at 15-40.
The 29-year-old missed the event for four straight years before a third-round loss in 2017, but has regained fitness in recent months and reached the semi-finals at the US Open last year, where he lost to Nadal.
On the resumption of play, Nadal held his two service points to take the second set 6-3.
His 6-4 6-1 6-2 victory means he has now reached his 24th Grand Slam final and equals Roger Federer's record for most finals at a single major - Federer's coming at Wimbledon.
It rarely is for Nadal at a place he has lorded over the way no other man ever has at any Grand Slam tournament.
It was the first time in three years that Nadal had dropped a set in Paris. "Good tactics and mentality in the first set". Nadal did not register a first serve in this segment of the match and he double-faulted in opening the fourth game.
By then, Nadal was finding his spots.
"You can win a set, but not a match against Rafa", said Del Potro keen not to over-egg any hint of weakness in Nadal's game.
The 16th-seeded Gauff, who is 14 years old, beat 15th-seeded Leylah Annie Fernandez of Canada 6-4, 6-3. At No. 72, he is the lowest-ranked French Open semifinalist since 1999.