In the other remaining quarterfinal, which will continue Thursday at Court Suzanne Lenglen, No. 3 Marin Cilic and No. 5 Juan Martin del Potro were at 5-all in a first-set tiebreaker when the play-ending shower came.
But Nadal insists he is ready for the fight on Sunday.
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 has now won 24 of his 27 Grand Slam semi-finals as he swept aside the threat of the Argentine in clinical fashion to set up a meeting with Dominic Thiem - the only man to have beaten him on the dirt in 2018 - in Sunday's final. "And in the end, I got it, and now I'm having a great present, looking forward for the future". He played some fantastic aggressive tennis to get through Djokovic in the quarters, just like he played unbelievable aggressive tennis to get to the quarters.
Nearly the best any player can hope for at Roland Garros is to merely trouble the clay-court master, to make him slightly uncomfortable and perhaps even win a set, as Schwartzman did, before the inevitable Nadal victory comes to pass. He required treatment on a hip problem suffered early in the first set and visibly wilted in the second, raising his arms in mock celebration when he won a solitary game while already 5-0 behind. After holding there, Nadal broke del Potro to take that set and was on his way, taking 14 of the last 17 games.
He has dropped just one set so far - at the start of his quarter-final win against Diego Schwartzman - and crushed 2009 US Open champion Del Potro in dominant fashion.
"Thiem is an awesome player".
The fourth set went hurriedly with serve until 5-5, when from out of nowhere Del Potro fashioned three break points. I have had three surgeries on my left wrist and I was close to quitting.
At World No 72, the Italian is the lowest-ranked French Open semi-finalist since 1999. "It has been a long time without good feelings".
Schwartzman led 6-4, 3-2 with a break of serve on Wednesday when the rain first came down, but he was two points from losing the second set upon returning on Thursday, and Nadal duly wrapped it up in no time.
"It was a really close tiebreak and I didn't want that especially after I missed an easy volley at 6/4".
At long last, Thiem converted his fifth set point when Cecchinato sent a forehand long. We have officially run out of superlatives to describe this man's clay court greatness, and we've also run out of intra-tennis comparisons.