Nadal beat Sinner 7-6 (4), 6-4, 6-1 in the quarterfinals on Tuesday at Roland Garros. He will face Argentine Diego Schwartzman in the semifinals Friday.
Schwartzman beat Nadal in straight sets on Sep. 19 at the 2020 Italian Open, his only win over Nadal in 11 career matches.
"I have two days to practice the things that I need to improve on. That's what I'm going to do," Nadal told reporters.
Nadal dispatched of Sinner in two hours and 49 minutes. He had one double fault, won six of eight break points, fired 37 winners and had 33 unforced errors. Sinner had three double faults, 31 winners and 44 errors.
Sinner and Nadal went back and forth in the first set before Sinner won the 10th and 11th game. Nadal then forced a tie break before he won the 72-minute set on a Sinner unforced error.
Nadal and Sinner exchanged game wins to start the second set before Sinner won the third and fourth games. Nadal responded with wins in the fifth and sixth games before Sinner won the seventh game to take a 4-3 lead. Nadal then won the final three games and won the set on another Sinner error.
Nadal dominated the third set and won the first four games before Sinner claimed the fifth game. The Spaniard fired a winner to claim the sixth game before he broke Schwartzman to win match point.
Schwartzman -- the No. 12 seed -- advanced to the semifinals with a five-set marathon win over No. 3 Dominic Thiem. The Argentine beat Thiem 7-6 (1), 5-7, 6-7 (6), 7-6 (5), 6-2 in the five-hour, eight-minute thriller.
"If I see the history, I'm 10-1 down [in matches against Nadal]," Schwartzman said. "I'm not sure if I'll have a lot of confidence, but I know that I can beat him."
The women's semifinals start Thursday with Iga Swiatek in a match against Nadia Podoroska. American's Danielle Collins and Sofia Kenin match up Wednesday in a women's quarterfinal. The winner of that match will face Petra Kvitova in the semifinals.
Kvitova -- the No. 7 seed -- beat Laura Siegemund in straight sets Wednesday to reach the semifinals.
The women's singles final is Saturday at Roland Garros. The men's final is Sunday.