"I played so solid all the time, hitting the ball so hard," said del Potro. "I saw Rafa playing very far off the baseline, which is good for my game, for my serve, and confidence. That's the way to beat this guy."
And he said he could play even better after serving just five aces against Nadal.
"I didn't make too many aces for playing against the No1 in the world," he said. "That's what I need tomorrow against Djokovic. I need to win easy points with my serves. Hopefully, my forehands and backhands work like today in the final. I'll be aggressive like today."
Dominating from the baseline on both forehand and backhand sides, del Potro raced into a 4-0 lead in the first set as Nadal desperately searched for a foothold.
A single break was enough in the second set for the 1.98m Argentine, who hit a total of 28 winners and 31 unforced errors, landing 80 per cent of first serves in his victory, which also secured him a place at next month's World Tour Finals in London.
A rueful Nadal, who uncharacteristically failed with all six of his break point opportunities, admitted that he was beaten by the better player.
"Very few times I have played against a player with a level like today I played against ... At the end I played against a player who served 80 per cent of first serves, who hit every ball as hard as he can I think, and with no mistakes," said the 27-year-old.
In the first semifinal, Tsonga landed just 46 per cent of first serves in an ultimately one-sided first set, and despite an improved showing in the second he cracked in the 12th game as Djokovic completed a straight-sets win.
"I think I raised my game today compared to last night's match," said Djokovic, who lost his cool midway through the second set over a couple of line calls before he found his focus again.
Nadal, Djokovic and David Ferrer have secured their places at next month's elite World Tour Finals, featuring the season's top eight players. Tsonga also hopes to secure one of the places.
Top results
6-Juan Martin Del Potro (ARG) bt 2-Rafael Nadal (ESP) 6-2 6-4.
1-Novak Djokovic (SRB) bt 7-Jo-Wilfried Tsonga (FRA) 6-2 7-5.
- AAP