Mitch Trubisky threw for 166 yards and led three scoring drives after Mike Glennon struggled for Chicago, before the Denver Broncos scored two long touchdowns in the closing minutes to beat the Bears 24-17 in the preseason opener on Thursday night.
Denver's Trevor Siemian did nothing to hurt his standing as the leader for the starting quarterback job, while Paxton Lynch did little to close any ground.
Third-stringer Kyle Sloter threw a 47-yard touchdown pass to Isaiah McKenzie with about six minutes left in the game, and De'Angelo Henderson ran for a 41-yard score with just under two minutes remaining to put the Broncos on top 24-17.
Trubisky replaced veteran Mark Sanchez late in the second quarter and completed his first 10 passes while leading Chicago to touchdowns on his first two possessions and a field goal on the next one. That gave the Bears a 17-10 lead.
Glennon had a rough time in his first appearance for Chicago. Signed to a three-year contract after the Bears parted with Jay Cutler, he was 2 of 8 for 20 yards with a zero QB rating. Chris Harris Jr. intercepted an overthrown pass on the game's third play from scrimmage and returned it 50 yards for a touchdown.
The Bears visit Arizona on Aug. 19.