The 11th-seeded Schwartzman appeared to have done his homework well as he dominated the early exchanges to bag the opening set - an achievement in itself as it was the first one Nadal had lost at Roland Garros since 2015.
I'll be back tomorrow to assess the ladies final, and again on Sunday to preview the men's final - I fully expect it to be Nadal v Thiem, but we shall see if Messrs Del Potro and Cecchinato can do anything about this. The most recent match was in the 2017 US Open, a match Nadal won in four sets.
Garbine Muguruza overwhelmed Maria Sharapova 6-2, 6-1 in a matchup of past French Open champions to reach the semifinals.
Del Potro's win over Cilic on Thursday was an emotional one for the sixth-ranked 29-year-old, who will return to the top four of the ATP rankings for the first time since February 2014 on Monday. "But at the same time, I think after the first rain delay, the match changed a lot because I played more aggressive with high intensity and the things were more on my side".
The delay enabled Nadal to regroup and he turned the deficit into a 5-3 lead before a second stoppage ended play for the day.
Interestingly, the match stats suggest there wasn't much between Del Potro and Cilic, with Del Potro only having two more break point chances than the Croat, and the 54% points won percentage is not particularly impressive for a 3-1 success. Only one of his wins at Roland Garros this year has been decided via straight sets, but a common theme seems to be that he's got better as matches have got longer. Both matches had been stopped by rain on Wednesday.
The fourth set went hurriedly with serve until 5-5, when from out of nowhere Del Potro fashioned three break points. "I felt that I was playing a little bit under more stress than usual, and he was able to take control of the point too many times", Nadal said about the match's start. I had surgery three times on my wrist and I was close to quitting this sport.
"It was a very hard match, Diego is a good friend and a good player", said the 16-time Grand Slam champion.
"Mentally things can be better or worse, but the determination I had yesterday, it created great impact in the result and in the game".
Top-ranked Simona Halep is up against 2016 champion Garbine Muguruza in the other semifinal match.
Otherwise, he stayed steady in a 7-6 (5), 5-7, 6-3, 7-5 win over No. 3 Marin Cilic in a matchup between two past U.S. Open champions.
"I thought that after nine years I [would] play [someone] different, not Rafa or Roger", del Potro said, with a smile. But she fell apart and eventually lost to the unseeded Latvian in her second French Open final. I am so proud to be playing tennis.