But Nadal's domination on the Roland Garros clay, where his record now stands at 85-2, is without equal and he will be a huge favourite to beat Grand Slam final debutant Thiem.
Such is his motivation to win his 17th Grand Slam on Sunday, that the task facing Austrian 24-year-old Thiem was described as "almost impossible" by Del Potro.
"He's a big favorite against everybody", said Thiem, who reached his first Grand Slam final by ending the out-of-nowhere run of 72nd-ranked Marco Cecchinato of Italy 7-5, 7-6 (10), 6-1.
The fifth seed, playing in his first Roland Garros semi-final in nine years, had three break points in the third game and three more in the ninth.However, the 29-year-old was unable to capitalise and Nadal made him pay in the 10th game when he claimed the opener off a netted backhand.
In a clash between the undisputed king and the only man who has offered a contest to his mastery of the clay courts, Rafael Nadal takes on Dominic Thiem for the biggest prize of them all, Roland Garros.
The seventh seed lost to Nadal at the semi-final stage in the French capital a year ago however and will be in uncharted territory when he plays the defending champion.
"If you tell me seven, eight years ago that I will be here. having this trophy with me again, I will tell you that is something nearly impossible", Nadal said.
Nadal, a 16-time Grand Slam champion, claimed his 85th win here against just two losses after weathering a big-hitting opening from 2009 US Open victor Del Potro to win 6-4, 6-1, 6-2. I know I have to play my best tennis to have a chance on Sunday.
But at 4-5 Thiem's serve let him down badly, handing Nadal three set points.
Ah, but there's a reason Nadal is 11-0 in semifinals at the French Open, a reason he is 10-0 in finals there - so far. "I think he's the second or third-best player on red clay", Cecchinato, who was suspended for match-fixing in 2016 before being cleared on a technicality, told reporters.
"But I have a plan". If Thiem can not find the court enough with his attempted winners, then the match will swing in Nadal's favour.
"Just thinking in a positive way and just thinking that I have to hold". Over the past two years, including best-of-three matches, the Spaniard is 49-2 at clay tournaments.
In Madrid, Thiem said the key was to be positive against Nadal. After serving a fault, Nadal took the unusual step of heading to the sideline in the middle of a game. "If I want to beat him, I have to play that way like I did in Rome and in Madrid".
"It was a very hard first set and Juan Martin had lots of opportunities".
Siniakova was the doubles runner-up at last year's U.S. Open with a different partner.
Nadal, in an on-court interview, also said he's sure that runner-up Thiem will win the tournament in "the next couple of years". One down-the-line forehand victor landed right at the baseline, leaving Thiem sagging his shoulders and muttering.More news: Avengers: Infinity War Passes $2 Billion Mark
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