Campbell, who also had one interception, played the first half while Kyle Boller took snaps in the second. Boller completed 7-of-9 passes for 55 yards and also ran for a score for the Raiders, who have won both their preseason games so far, both of which were on the road.
Oakland trailed 14-13 at halftime, but pulled away in the third quarter, when Slade Norris recovered a fumble in the end zone and Boller took a two-yard plunge across the goal line.
Michael Bennett powered Oakland's running game with 64 yards on 15 carries, while Louis Murphy caught three passes for 53 yards.
In two quarters of action, Jay Cutler threw for 99 yards and one touchdown on 7-of-15 passing for the Bears, who have dropped both their preseason matchups. Matt Forte rushed for 109 yards for Chicago, with the majority of them coming on an 89-yard touchdown run in the first quarter.
Bears linebacker Brian Urlacher left in the first quarter with a left calf injury and did not return, and the extent of the injury is not known.