"It's been an amazing season for me and I'm so happy to get a chance to fight for another title after a couple of seasons with injury troubles," said Nadal, who won a record-extending 10th French Open title in June.
"It means a lot to me. I had to change a couple of things after the first set because I was playing on his backhand too much and he was waiting for me there.
"So I tried to move him around more and be more unpredictable. I was not playing bad in the first set but I lost it so some things had to change."
The 31-year-old was already the favourite coming into the tournament but those odds shortened when Del Potro knocked out Roger Federer in the quarter-finals.
The Argentine surprised those with concerns over his fitness – following the Federer match, an epic five-set win over Dominic Thiem and a bout of flu – with a superb performance to take the opening set.
Del Potro’s backhand, so often his weak point following wrist surgery, proved to be the biggest surprise as he caught Nadal out on a number of occasions to blow the match wide open.
However, those doubters were soon proved right as Nadal stormed back and overwhelmed Del Potro to win the second set with a bagel.
Del Potro, clearly far from 100 per cent, put up more of a fight in the third but once Nadal got his break in the second game, the eighth of nine games he won in a row, he wasn’t going to give it up.
The Argentine dug deep in the fourth as more booming forehands came out, but just when he was threatening to start another remarkable turnaround Nadal stepped up and was suddenly buzzing around the court.
The Spaniard's relative freshness in terms of hours played showed and he blew Del Potro away to seal an impressive victory.
He will now face slam final debutant Kevin Anderson after the South African also came from behind to beat Nadal’s compatriot Pablo Carreno Busta in the other semi-final.