Nadal trailed 6-4, 3-5 last night when rain saw the match suspended and eventually postponed until today.
But the sun shone on Thursday and the No 1 seed revelled in the drier conditions, losing just four games as he ran out a 4-6, 6-3, 6-2, 6-2 victor.
And he admitted he was forced to go for his shots a bit more in the second “half” of the match.
“Diego is a good friend and it wasn’t easy,” Nadal said.
“After the rain, I played at a better level, more aggressive. I’m so happy to make it to the semi-final and thanks to the crowd for their support.”
And Eurosport pundit and former world No 4 Greg Rusedski agreed that Nadal had played more aggressively on the second day of play, especially on his serve.
“You look at Rafa after that first rain delay, he comes back, serves better and hit the ball harder,” Rusedski said.
“But tactically today he was going a lot more back behind Schwartzman, which was very, very clever tactically. This is why he is such a champion. He keeps Schwartzman off balance early on in rallies.
“Another thing he did well: he served a lot faster than he did yesterday.
“Conditions were a lot more fine. The ball was sailing around, going harder. And that really suits Rafa. As soon as he went on the forehand side, he went to the backhand, opening up Schwartzman.
“Tactically that was very astute.”
Nadal will now face either Marin Cilic or Juan Martin del Potro in the semi-final, leaving him two wins away from a remarkable 11th title.
But the Spaniard is taking nothing for granted despite having been an odds-on favourite to take overall victory at Roland Garros even before the tournament started.
“I’ll play tomorrow again and it’s always a great emotion to play here,” Nadal said.
“It will be very difficult match whoever I play.”