In the other semi-final, Marco Cecchinato's unusual run in the last two weeks was ended by Dominic Thiem, also in straight sets, although the first two sets were somewhat closer than anything Del Potro could muster.
The result also marks the sixth consecutive Grand Slam won by either Nadal or Federer.
Not that 17-times Grand Slam champion Nadal, whose latest feat is all the more remarkable considering he was sidelined for several weeks this year due to injury, is pre-occupied with trying to keep up with his Swiss rival. Thiem looks like he belongs on the big stage - but will he take that confidence into a showdown against Nadal who has only ever lost twice on the big Philippe Chatrier Court? A massive part of Nadal's legend on clay is that he makes players, however good, however aggressive, play on his terms.
Rafael Nadal has for a long time been the King of Clay, but he's taken his dominance to new heights with his 11th French Open win.
Here are the list of numbers behind Rafael Nadal's 11th French Open crown.
Why? Nadal was 95-0 when capturing the opener on clay in the best of five format. Only Thiem's 2016 victory over Nadal in Buenos Aires was a success on non-quick clay.
But Nadal held with some clever drop shots and after taking the second set it merely became a race against time to finish off Thiem before the rain arrived.
Up a break at 2-1 in the third set, Nadal stopped serving after a fault because he couldn't straighten his left middle finger. In the fourth game of the third set, he had the physio attend to his left hand because a finger cramp was making it hard for him to grip the racquet.
Such is his motivation to win his 17th Grand Slam on Sunday, that the task facing Austrian 24-year-old Thiem was described as "almost impossible" by Del Potro.
'Of course I would love to have 20 like Roger in the future or even more, but being honest, is something that is not in my mind. Thiem was hammering every ball that he could, and Nadal was responding with his classic clay court defense.
The Spaniard now inches closer to Roger Federer's all-time record of 20 Grand Slam titles.
And he increased the tempo further, consigning Thiem to defeat in his first major final when the Austrian sent a return long.
Nadal was rampant when he broke early in the second, but Thiem raised his game to force a break point when Nadal served at 4-2 - a game in which the Spaniard was warned for slow play.
Thiem was considered the stiffest test for Nadal at the French Open and understandably so.
The number of Masters 1000 titles won by Nadal, the most by a single player since the series began in 1990.