Prater's boot of 59 yards with 3 seconds left in regulation forged a tie and his 51-yard kick 8:34 into the resulting overtime handed another come-from-behind win to quarterback Tim Tebow and the Broncos (8-5).
Tebow engineered pressure drives before both kicks, using his skills to pull out a comeback for the fourth straight week while helping Denver surge into a two-game lead atop the AFC West.
Denver erased a 10-0 deficit in the fourth quarter, with Tebow hitting Demaryius Thomas (seven receptions, 78 yards) for the Broncos' only touchdown on a 10-yard pass with 2:08 left.
Caleb Hanie was limited to 12-of-19 passing for 115 yards as the fading Bears (7-6) dropped their third in a row.
Marion Barber picked up 108 yards and a touchdown on 27 carries but fumbled on the first series of overtime, setting up Prater's winning kick.