Thiem reached his first grand slam final at Roland Garros with a comfortable defeat of Marco Cecchinato, meaning he will face Nadal after the 10-time victor swept aside Juan Martin del Potro in the second semi-final.
If there were any reason for a bit of intrigue entering Sunday, it was this: Thiem beat Nadal on red clay at Rome in May 2017 and again at Madrid last month.
After breaking Nadal's serve to take the ninth game, Schwartzman hit a forehand victor at 40-30 to take the first set 6-4.
Nadal broke in the lone game he had an opportunity to wrap up the set.
But fast-forward 12 days and the affable Del Potro is preparing to take on 10-time champion Nadal in his first French Open semi-final since 2009.
"I think it helps, definitely, knowing that you were the last guy to beat him", said Bresnik, whose association with Thiem spans more than 15 years. That began a run of four consecutive French Open triumphs through 2008.
Thiem‚ who was playing in his third successive French Open semi-final‚ admitted the second set had been a nervy encounter after needing five set points to get through it.
6-1 defeat of surprise semi-finalist Marco Cecchinato ended that miserable streak, and Thiem, who has already beaten Nadal on clay this season, could now face the defending champion in the tournament decider.
He takes on rising tennis star Dominic Thiem for the title.
The 29-year-old missed the event for four straight years before a third-round loss in 2017, but has regained fitness in recent months and reached the semi-finals at the US Open last year, where he lost to Nadal.More news: Reported Killed in Missile Attack in Saudi Arabia
Thiem has been to the semifinals in Paris three years in a row. A routine hold of serve by each player led to 5-2 and Nadal stepped up to serve for the set. Nadal did not register a first serve in this segment of the match and he double-faulted in opening the fourth game.
Nadal will retain the world number one ranking if he wins - but that will be the last thing on his mind.
Del Potro often had Nadal in trouble in a ferocious first set but paid heavily for failing to convert any of the six break points that came his way.
A few hours earlier, as Nadal and Thiem warmed up, the booming voice of the announcer at Court Philippe Chatrier detailed the bona fides of both.
The 16th-seeded Gauff, who is 14 years old, beat 15th-seeded Leylah Annie Fernandez of Canada 6-4, 6-3.
The top-seeded Nadal enters Sunday with a 10-0 record in title matches at Roland Garros and an overall career mark of 85-2 at the clay-court Grand Slam tournament.
Rafael Nadal bids for his record-extending 11th French Open championship when he faces Dominic Thiem in the final.
Throw in three titles at the U.S. Open, two at Wimbledon and one at the Australian Open, and Nadal is up to 17 majors, second among men only to Roger Federer's 20.
Del Potro, the US Open victor in 2009, is playing the tournament for only the second time since 2012 after a spate of injuries.