The Orioles handed the Angels a second straight setback to further damage their bid to catch the Texas Rangers in the American League West pennant race.
Los Angeles starter Ervin Santana (11-12) put the Angels in an instant hole and went on to lose his third consecutive decision.
He walked Matt Angle on four pitches to open the first and Hardy followed with his 27th home run of 2011.
Zach Britton (10-10) and two relievers made the 5-0 lead stand up. Britton allowed a run on three hits while striking out seven over seven innings to win for the fourth time in six starts.