Del Potro, seeded first and ranked 12th, won his second title of the year and 11th of his career.
"I felt it was my best match of the week," del Potro said. "I felt really confident on my forehand and I grew in confidence every game."
Gasquet, seeded second, also lost this clay-court final in 2007 when he faced Novak Djokovic. He dropped serve early in both sets. Del Potro didn't give up a break chance in the match and had six aces in improving his record against Gasquet to 4-1.
"He's very tall and has a good second serve and was hitting the ball very well," Gasquet said. "He was the better player today."