Cecchinato had never won a Grand Slam match before this year's Roland Garros but made the semis with a string of stunning wins.
"Nadal is still playing at only seventy-five per cent efficiency and that, still, is good enough for him to beat tough opponents like Juan Martin del Potro". It will be followed by the all-American matchup between Madison Keys and Sloane Stephens.
He saved three set points in the second before winning an epic tiebreak, something which Cecchinato has become famous for this year at Roland Garros.
That was swatted away with Nadal's double-handed backhand, though, and the second set duly went the way of the favourite.
He fired long on a first set point, Nadal saved the second with a jaw-dropping drop shot but on the third, just after the match was interrupted for a few minutes while an unwell spectator was evacuated, Schwartzman unleashed a stunning forehand victor down the line - his 20th victor.
Play in the men's quarterfinals has been stopped again due to rain at the French Open.
"As long as Rafa is healthy, it will be very hard to beat him here", del Potro said on Friday.
Nadal's incredible record in Paris now reads 86 wins and two defeats.
Thiem's confidence has grown as he reached the final of a major for the first time after falling in the semis in the last two editions of the French Open.
Breaking serve in the first game and bouncing to a 4-2 lead, Thiem controlled proceedings before Cecchinato reeled off the next three games with trademark flair and adventure.
Del Potro fought back tears during his post-match interview and was loudly cheered by fans at Court Suzanne Lenglen. When you're in a final like Roland Garros, it's a great happiness. He is 10-0 in French Open finals and 77-0 at the tournament overall when he wins the first set, so getting a jump on him early - a tactic far easier to write about than to execute - would seem to be a fairly obvious strategy.
Injuries have hindered the Spaniard's Wimbledon campaigns in recent years but assuming he comes through Sunday's final unscathed he could yet mount an assault on the SW19 title he has won twice before. 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.
Nadal had looked imperious on his way to a 12th quarter-final at Roland Garros, but the diminutive Schwartzman played with aggressive intent to rock the claycourt king.
"They are the first set is everything, and the weather is everything". "I missed a lot at the beginning of the match".
The world number one had looked out of sorts in damp conditions on Wednesday as Schwartzman bombarded him with winners to cause him all sorts of problems, with the Argentine leading by a set and a break when the players were first called off court due to rain.
Rafael Nadal has dropped a set at the French Open for the first time since 2015.
Top-ranked Simona Halep will have another shot in the French Open final.
Otherwise, he stayed steady in a 7-6 (5), 5-7, 6-3, 7-5 win over No. 3 Marin Cilic in a matchup between two past U.S. Open champions.
Thiem was quick to respond, reeling off the next three games to take the set in 46 minutes.
Kerber, a former USA and Australian Ooen champion and ex-number one is in her second quarter-final in Paris, six years after her first.
No player in history has won as many grand slam titles at a single tournament as Nadal has in Paris.
"If I want to beat him", Thiem said, "I have to play that way".
In the women's last-eight, Maria Sharapova faces fellow former Paris champion Garbine Muguruza.