Nationals starter Jordan Zimmermann had retired 13 straight batters before Nick Markakis led off the seventh inning with a single into right field. Vladimir Guerrero followed with a two-run homer on an 0-2 pitch, his fifth of the season.
Orioles 2, Nationals 1.
Guerrero pumped his fist as he approached first base, and he pointed to the sky before crossing home plate.
Guerrero had lined out and flied out before batting in the seventh, giving the Orioles the lead and improving his average to .311.
Jeremy Accardo had allowed runs in six straight outings before tossing a scoreless sixth inning in relief of Chris Tillman. Accardo gave up a leadoff single to Michael Morse, but he retired the next three batters.
Accardo has allowed 38 baserunners in 20 innings.
Jim Johnson followed with a scoreless seventh, though he also gave up a hit.
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Down on the farm, Triple-A Norfolk's Rick VandenHurk held Louisville to two runs and four hits over eight innings, with no walks and five strikeouts, but the Tides lost, 2-1. VandenHurk is 2-7 with a 5.29 ERA.