Trailing 3-0 after four innings, the Royals scored single runs in each of the next four frames, with Hosmer driving in two of them. The Royals first baseman began the rally with a run-scoring single in the fifth, and Billy Butler followed with a solo homer in the next inning.
Kansas City tied the contest on Humberto Quintero's RBI double in the seventh and, in the next inning, Hosmer chased home Mike Moustakas from third with a looper to left off Pedro Strop (3-2), finishing the day 3-for-4.
The rally made a winner of Greg Holland (1-2) while Jonathan Broxton racked up his ninth save for the Royals, who evened their three-game set.
J.J. Hardy and Chris Davis each knocked a solo homer for Baltimore, which came into the game tied with Tampa Bay for first place in the American League East.