Cutler threw a go-ahead 5-yard TD pass to Earl Bennett in the fourth quarter, Forte ran for 133 yards and the Bears (5-3) won their third consecutive game.
It was a crushing loss for Michael Vick and the Eagles (3-5), who blew a fourth-quarter lead for the fourth time this season. Jeremy Maclin fell down and was tackled at the Bears 30 after a 9-yard catch on fourth-and-10 with just under two minutes left.
The defending NFC East champions trail the New York Giants (6-2) by three games.
Chicago is third in the NFC North behind Green Bay (8-0) and Detroit (6-2).
The Eagles were trying to even their record with their third consecutive win after an awful 1-4 start threatened to ruin a season that began with Super Bowl aspirations.
It was the fifth consecutive year that the two teams have met. Chicago has now won four of those meetings, including a 31-26 victory at Soldier Field last November.
Philadelphia safety Nate Allen left the game after sustaining a concussion in the first quarter. He did not return.