Sousa came away a 2-6, 7-5, 6-4 winner by saving all six of the break points he saw in the second and third sets against Benneteau. It was the third consecutive seeded player Sousa knocked out. He beat world No. 4 David Ferrer in the quarterfinals and took out fourth seeded Jurgen Melzer in Saturday's semifinals. Benneteau was seeded fifth.
Benneteau won two-thirds of the points on serve but was unable to convert any of his break chances in the second and third sets while Sousa had one in each set for the win.
Sousa, 24 years old and No. 77 in the world, is the seventh first-time winner on the tour this year and the first player from Portugal to win an ATP tournament.
The frustration in title matches continues for Benneteau, who is 0-9 in finals. He has been in at least one championship match each year since 2008, including two this year, but is yet to win.
The first-place check for $158,000 pushes Sousa's career winnings to more than $700,000. Benneteau took home $83,240 as the runner-up and has won nearly $6 million in his career.