Hardy led off the inning with his 19th homer of the season, a drive to left field off Kansas City southpaw Jeff Francis.
Francis had retired Hardy twice before that at-bat, leaving the Orioles' shortstop in a 2-for-26 slump.
The Orioles have battled all the way back after falling behind, 3-0, in the first.
Left-hander Zach Britton has allowed one earned run and eight hits, with no walks and three strikeouts. He threw 24 pitches in the first inning, and he's up to 66 through the fourth.