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 (5-3) won its third straight game, but remains third in the NFC North behind Green Bay (8-0) and Detroit (6-2).
After LeSean McCoy's 33-yard touchdown run following Forte's second fumble gave the Eagles a 24-17 lead in the third quarter, the Bears answered with 13 straight points.
Robbie Gould kicked a 38-yard field goal to cut it to 24-20, and then Chicago's defense forced a punt after three plays.
The Bears drove 51 yards for the go-ahead score with Cutler tossing a 5-yard TD pass to Bennett over Asante Samuel for a 27-24 lead.
The Eagles reached the Bears 42 on their next drive. On fourth-and-6, punter Chas Henry bounced a pass to a wide-open Colt Anderson and Chicago took over.
Henry spent a lot of time throwing passes to long snapper Jon Dorenbos on the sideline in the second quarter, presumably warming up for the fake punt. He got his chance and badly underthrew the pass.
The Bears took advantage. A pass interference penalty on Nnamdi Asomugha at the Eagles 7 prolonged the drive. The defense stiffened and Gould hit a 22-yarder to extend the lead to 30-24.
Trent Cole knocked the ball loose from Forte following a 6-yard run midway through the third quarter, and Mike Patterson recovered at the Bears 41. Forte was originally ruled down, but the play was overturned when the Eagles challenged.
Two plays later, McCoy sprinted down the left side and into the end zone to score for the eighth straight game, tying Hall of Famer Steve Van Buren's club record.
In a matchup featuring two of the game's best running backs, Forte outplayed McCoy except for the two fumbles.
McCoy had 71 yards rushing.
The Eagles tied it at 17 on Ronnie Brown's 4-yard TD run that capped an 80-yard second-half opening drive. The TD was Brown's first since joining the Eagles. Brown was one of six former Pro Bowl players acquired by Philadelphia in the offseason. He hadn't made much of a contribution and was traded to Detroit last month only to have the deal voided because Jerome Harrison didn't pass a physical.
The Bears took a 17-10 halftime lead on Marion Barber's 2-yard TD run after a costly fumble by DeSean Jackson.
Jackson, a Pro Bowl punt returner, was stripped by Corey Graham and the Bears recovered at the Eagles 9 with a minute left in the second quarter.
A roughing-the-passer penalty on Jason Babin gave Chicago a first down at the Eagles 2 after Cutler threw an incomplete pass on third down. Barber then ran in from the 2.
Cutler threw a 5-yard TD pass to Matt Spaeth and Gould kicked a 51-yard field goal to help the Bears build an early 10-0 advantage.
Rookie Alex Henery kicked a career-high 47-yard field goal for the Eagles, and the defense made a big play on Chicago's ensuing series late in the second quarter.
Forte caught a short pass from Cutler, but Brian Rolle punched the ball out. Rolle picked it up and ran 22 yards for a TD that tied it at 10.
After struggling badly against the run the first five weeks, the Eagles improved in the past two games. They allowed just 127 yards rushing combined in wins against Washington and Dallas.
Helped by a pass interference call on Major Wright that kept their second drive going, the Eagles reached the Bears 19 early in the second quarter. But Vick made a poor throw into double coverage that was picked by Wright, who returned it 36 yards to the Bears 48.
The teams met for the fifth straight year. Chicago has won four of those games. Beloved former Eagles coach Buddy Ryan was honored at halftime.
Vick was 21 of 38 for 213 yards and one interception. He fell to 0-4 as a starter against the Bears.
Cutler was 18 of 32 for 208 yards and two TDs.
Ryan, who is battling cancer, was Chicago's defensive coordinator during their Super Bowl championship season in 1985. He came to Philadelphia the next season and led the Eagles to the playoffs in 1988-90.
Ryan got a loud ovation and fans chanted "Buddy! Buddy!"