"Four years ago, I didn't know if I would be back in a final," Nadal told reporters. "So I can't think about that. I know he has great potential. I know he's a great player."
Nadal dominated the Argentine in three sets, beating him 6-4, 6-1, 6-2 in the clay court bout. Thiem beat Marco Cecchinato 7-5, 7-6, 6-1 in his semifinal matchup.
"When you don't take your chances against the No. 1 in the world, you are are in trouble," del Porto said. "That happened today."
Nadal is now 10-5 in his career against del Porto. Del Porto's last win against the Spaniard came at the 2016 Summer Olympics.
"Rafa is playing every point better, from the beginning to the last point of the match," del Porto said.
Nadal beat Stan Wawrinka in the 2017 French Open. His other titles at Roland Garros came in 2005, 2006, 2007, 2008, 2010, 2011, 2012, 2013 and 2014.