There were six home runs in the game, one of them being the 40th of the year for Baltimore's Chris Davis.
The Orioles, who have won three out of four, had a 7-6 lead heading into the bottom of the sixth. Baltimore, however, loaded the bases on consecutive singles by J.J. Hardy, Henry Urrutia and Ryan Flaherty to open the inning.
McLouth followed with his home run to right that opened a five-run cushion.
Chris Tillman (14-3) picked up the win despite giving up six runs on eight hits in 5 1/3 innings. He has captured four starts in a row.
Aaron Harang (5-10) allowed seven runs on seven hits while working five innings to take the loss. It was the fourth straight setback for Seattle.