A straight-sets victory over the Frenchman has set up a meeting with Roger Federer in Sunday's final but Del Potro believes he must eradicate the mistakes on his serve if he is to beat the world number one.
The Argentinian said: "It was almost perfect today.
"I was very pleased with my serve. But I still have work to do, I had two double-faults in the second set. If I want to win the title, I can't have that."
Federer, who has a 13-2 career record over Del Potro, booked his place in the final with a comfortable win over Paul-Henri Mathieu.