Schwartzman had managed his first victory over Nadal in 10 meetings at the Italian Open in Rome last month but a repeat never looked on the cards in the Spaniard’s fortress.
Nadal’s 6-3 6-3 7-6 (0) victory made it 99 wins and only two defeats at Roland Garros and he will challenge for a 13th title on Sunday.
Victory would give him a 20th grand slam crown, drawing him level with Roger Federer at the top of the all-time list, and few would bet against him.
He was relentless for two and a half sets but a faltering finish will be a cause for optimism for whoever he faces in the final on Sunday.
From 4-2, Nadal’s grip on the match loosened and he had to save three break points at 5-5 before clinching the match on a tie-break to ensure he reached the final in Paris without dropping a set for the sixth time.
The Spaniard said: “Today I think the experience of Rome helped me in some way because I was able to take a look on the match, to analyse the things that worked well and things that, of course, didn’t work.
“We tried to go on court with a plan, with the right determination. In some way I think I played tactically the right match.
“I think I made a couple of mistakes tactically and of course technically. But, in general terms, I am super happy about the match.
“It has been an important victory for me against a very tough player. To win against Diego, you have to work a lot and you have to play well for such a long time.
“That’s what I did today. I think I played solid. I played with the right determination in most of the moments of the match.
“Especially in the tie-break, I finished the match playing well. I needed to be a little bit more aggressive in the (second) half of the third set when I had the score in my favour.
“I lost a couple of opportunities there to close the match before and to not suffer like I suffered at the end.”
The crux of the match in many ways was a first set that averaged more than seven minutes a game. Nadal was largely conservative, using extra height on his shots to counteract the lack of spin caused by the cool, damp conditions.
Schwartzman had four break points but could only convert one while Nadal struck on both of his two chances, wearing the Argentinian down with his consistency and going to his attacking arsenal only when necessary.
Schwartzman lacked the attacking intensity he had shown in Rome, which was perhaps a legacy of his five-hour victory over Dominic Thiem in the quarter-finals.
He looked down and out at 1-3 in the third set but dug in admirably, breaking Nadal twice in succession to pull back to 4-4. Now it was Schwartzman dictating much of the play but, with the Spaniard’s hold for 6-5, the door was closed.
Schwartzman said: “He played better than Rome. He has a lot of matches right now in his body, so it’s better for him.
“Maybe I made a few mistakes with my backhand today. I was not really aggressive with the backhand. But Rafa is Rafa. I think he knows how to improve. He knows how to practise, how to do everything.
“After Rome, he goes straight to practise. He went to improve the things that he did bad in Rome. That’s why he’s in the final right now.”