Matt Prater kicked two field goals of 50 yards yard make coming with 8:34 left in overtime, to 10.
Tim Tebow continued his magic run for the Broncos (8-5), who surged into first place in the AFC West.
The Florida product led the charge from a 10-0 fourth quarter deficit, ending with 236 yards passing and one touchdown while adding 49 rushing yards.
Caleb Hanie threw for 115 yards on 12-of-19 passing for the Bears (7-6), who have dropped three in a row.
Marion Barber totaled 108 yards and a touchdown on 27 carries, but made a tactical error late in regulation which led to Prater's game-tying field goal and also coughed up the ball on the first series of OT which led to Prater's winning kick.