At two sets down it would require a virtual miracle for the 24-year-old to win but the fight was still evident in Thiem, who held from 0-40 down to kick start the third.
Diego Schwartzman has come closest this fortnight to become the third man to beat Nadal in Paris.
A year later he exacted his revenge over the Swede, but this time in the final for his fifth Roland Garros title.
"It's really incredible. I played a great match against a great player", said Nadal.
While it may be a few years until Nadal is no longer at the peak of his powers on clay, Thiem looks like a worthy successor to the Spaniard.
"Maybe I'm sleeping. It's wonderful, it's unbelievable for me". Today was very humid against a player who pushed me to the limit.
Won his second Grand Slam of 2017 at Flushing Meadows after a 10th French Open title in June.
Cecchinato's match-winning performance against Novak Djokovic this week is probably the finest tie-break ever played on clay, as Aussie doubles great Peter McNamara suggested when he tweeted immediately afterwards that it had showcased all the finest qualities of clay court tennis.
"But I'm also aware that here it's tougher". So I think this is the best moment for me. In both competitions the first seeds have reached the deciding stages, with the semi finals in the ATP competitions scheduled for Friday. The odds are also low for the player from Spain to win in straight sets. Across the other slow-medium clay venues - Monte Carlo, Barcelona and here - Nadal has utterly schooled Thiem.
He made Djokovic pay for that failure to convert when he reeled off four successive points in the ensuing tiebreaker.
If there was a scare for Nadal it was an outbreak of cramp in his left hand in the third set, which he managed to shake off, like everything else this fortnight.
While that was happening, Cecchinato was docked a penalty point for unsportsmanlike conduct after a lengthy argument with the umpire and supervisor for leaving the court without permission. He lost the first set, then turned things around after a rain delay. Like McEnroe in 1980, Federer would win the fourth set tie-break, which would include a backhand victor by the Swiss to save a second match-point against him that ranks among his finest ever shots, but would ultimately lose the match. Corrado Barazzutti achieved the feet by entering the Roland Garros semifinals in 1978.
Rafael Nadal and Dominic Thiem at the French Open in Paris. The clay of Paris is the clay of Nadal, who has fallen in victory six times to his back and thrice to his knees, plus the two occasions standing, winding up 10 times behind the baseline and one sprawled between the service boxes, living a single dream of many so very many times.
Thiem's serving and shot-making under pressure were among his principle weaknesses in losing the first set.
Zverev said he will undergo an MRI to discover the seriousness of his injury. He converted the second to make the score 2-1. He survived a couple of early scares at the French Open this year, but he is likely to outshine Marco Checchinato.