Mauresmo, ranked fourth by the WTA Tour, won her third title this year and 18th overall. She came off consecutive opening-round losses at Moscow and Zurich.
Two points from losing the match, Mauresmo took control when Dementieva's serve broke down. Dementieva double faulted twice in the 10th game, including the decisive point that allowed Mauresmo to even the third set at 5-all.
Mauresmo used a strong forehand to hold serve in the next game and finished off the match by forcing errant shots from Dementieva.
The Frenchwoman's path to the final was helped by the withdrawals of top-seeded Lindsay Davenport and Maria Sharapova earlier in the week, leaving her the highest-seeded player.
Serena Williams, Venus Williams and Patty Schnyder also withdrew because of injuries. Steffi Graf is the only other three-time Advanta winner. She did it in 1992, '95 and '98.
Dementieva, looking for first title this year, dropped to 4-10 in career finals. She double faulted 14 times, yet nearly came out the winner.
Mauresmo is scheduled to join Dementieva, Davenport, Schnyder, Kim Clijsters, Mary Pierce, Nadia Petrova and defending champion Sharapova at the WTA Tour Championships that begin Tuesday in Los Angeles.
The Advanta tournament ended its 21-year run at Villanova, AP reports.