Bush racked up 104 yards on 26 carries and Tyvon Branch iced Oakland's first win over the Chargers in 13 games with a 64-yard fumble return for a score.
The Raiders (2-3) downed San Diego (2-3) for the first time since Sept. 28, 2003. They got 159 passing yards and a touchdown from Jason Campbell, who came on in relief of injured quarterback Bruce Gradkowski.
Zach Miller corralled six passes for 62 yards and a score and the Raiders blocked two punts in the contest.
Philip Rivers amassed 431 yards and two TDs on a 27-of-42 passing performance, with eight going to Malcom Floyd en route to a 213-yard game.