After a tough first set, Nadal jumped out to a 5-0 lead in the second set and rolled, 6-4, 6-1, 6-2.
Looking ahead to the final and recalling Thiem's victory over Nadal in Madrid, a exhausted del Potro uttered: "Maybe on Sunday (Thiem) can repeat".
Seventh seed Thiem, who will be playing in his first grand slam final, is regarded as second only to Nadal on clay - albeit probably quite a distant second.
His remarkable run-remember, he won his first-round match 10-8 in the fifth set-is offset a bit by these allegations. For me it's incredible.
"That's why he's the No. 1 and beating all the guys", added Del Potro after his 10th defeat in 15 meetings with the 32-year-old Spaniard.
"I couldn't play my best because of him", said del Potro, the 2009 U.S. Open champion. I hope to be ready to do it.
Nadal's backhand was doing most of the damage, with three winners having set up the double break on his way to a two-set lead, and Del Potro was broken to love in his first serve game of the third, with Nadal inflicting a devastating backhand victor up the flank after another majestic defence.
"It was even heavier and more overcast than I even remember it being". The vanquished del Potro acknowledged as much as he reflected on the brief stretch where he was able to put up some resistance to Nadal's unremitting intensity.
Surely, so did del Potro.
Asked about facing Nadal, who he has beaten five out of 14 times but never on clay, he was drowned out by his fans who clearly believe in their man's chances.
The No. 7-seeded Thiem beat Cecchinato 7-5, 7-6 (10), 6-1 in the semifinals Friday. He has already won titles in Rome, Barcelona, and Madrid while the only loss came in the quarter-final of Madrid Open against fellow French Open semi-finalist, Dominic Thiem.
Cecchinato's bid to become the spoiler's spoiler ended, for all intents and purposes, when he was unable to convert any of three set points in an entertaining second-set tiebreaker that was the middle chapter of Thiem's 7-5, 7-6 (10), 6-1 win.
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"If lost that tiebreak it would have been a very close match I think and I didn't want that".
Nadal should be favourite, of course - his experience of the big stage and pre-eminence at the French Open presents a significant obstacle for his young opponent to overcome - but it's important not to overstate Nadal's dominance.
"Then you lose, you lose, but I gonna play with my highest passion and love for the game and for the sport to try to have success". Stephens won last year's US Open; Halep is 0-3 in major finals.
"Once he gets ahead in the match, his confidence gets back", said Moya, the 1998 French Open champion.
The Austrian netted an easy volley to give another opportunity to Cecchinato, which he seized, forcing his opponent to a backhand error.
But an industrious Thiem responded with a strong hold and broke back at 5-5 with a sizzling forehand victor down the line, and served out the set in just 45 minutes.
The Spaniard had won a tight first set with a score of 6-4.
It looks a daunting mission for the 24-year-old Thiem but not necessarily an impossible one.
"I was lucky or - lucky or I don't know what to say for them".
"Otherwise, it's not a very nice feeling".
"I can take some things off (those wins)".