It will be followed by the all-American matchup between Madison Keys and Sloane Stephens.
On Wednesday, Schwartzman had come on court swinging and he succeeded in spraying winning shots off both wings.
The match was finely poised after the overnight rain delay, with nothing to split the pair at 5-5 in a tiebreak, but Del Potro reeled off two points in a row to clinch the first when play resumed on Wednesday. Tomorrow men's singles quarterfinals and women's singles semifinals!.
It took Nadal just two quickfire points to wrap up the set and leave the two players with effectively a best-of-three set match to play on Thursday.
He was serving in the fourth game when he went back to his chair and unwrapped strapping on his left wrist.
The Spaniard continued his extraordinary domination at Roland Garros with a ruthless 6-4 6-3 6-2 victory.
Nadal was far from his usual impeccable self on red clay, too.
Nadal is now 85-2 for his career at Roland Garros, with a record 10 championships.
"Thiem is an incredible player". He has won every final he has reached, and in those 11 finals he has dropped just six sets.
More prize money is up for grabs than ever before at this year's French Open but it remains the least lucrative of the four Grand Slams for players to win.
"Even if it was 6-3 6-4, it was an uncomfortable match for me". She reacted well to limit her mistakes while staying aggressive on her German opponent's service games.
He led by two sets plus a break early in the third, when the middle finger on his racket-wielding left hand was cramping so badly he couldn't straighten it. "The match changed a lot", he said. Still, I know how to play against him.
Anything can happen in a Grand Slam final.
But if there is a tad of intrigue entering this final, it is because of what happened in Rome on May 19, 2017, and in Madrid on May 11, 2018.
The German left-hander had lost in the first round in the last two years.
The world number one has won all five of his meetings with 11th seed Schwartzman.
Second-seeded Olivier Marach of Austria and Mate Pavic of Croatia are through to the French Open men's doubles final, beating 2016 champions Feliciano Lopez and Marc Lopez of Spain 6-4, 7-5.
The first Austrian to reach a grand slam final since Thomas Muster triumphed here in 1995, Thiem struggled to fend off the world No.72 before easing to a 7-5 7-6 (12-10) 6-1 success. Looking at the bigger picture, Nadal hadn't ceded a set in Paris since 2015, when he lost to Novak Djokovic in the quarterfinals.
Nadal, in an on-court interview, also said he's sure that runner-up Thiem will win the tournament in "the next couple of years".
She needed only 70 minutes to eliminate Sharapova and dominated her with superb returning, breaking the former No. 1 a half-dozen times.
"I want to work more to go top 20".
A visibly dejected Schwartzman took only one point on his serve before losing the fifth game while Nadal held to lead 5-1.
A hold to love showed Thiem had not given up the ghost, however unlikely a repeat of Simona Halep's heroics from the same position a day earlier seemed.