The Athletics have dropped three in a row and have lost seven of their last eight. They were unable to solve Chin (2-2), who struck out five and walked two while throwing 106 pitches.
The game was scoreless until the seventh, when J.J. Hardy led off with a single for the Orioles and reached second when Josh Reddick misplayed the ball in right field. Steve Pearce then delivered a one-out single off Tommy Milone (3-2) to drive in the game's first run.
Jim Johnson relieved Chen in the ninth and surrendered a hit on his way to his ninth save.