Garrett Olson (3-0) allowed nine hits and three runs in five innings, but he got the win thanks to a solid effort from the Orioles' bullpen.
The game was tied at 3-3 going into the Baltimore fifth, which Roberts opened with a three-base hit. Melvin Mora, who had missed two straight games with a sore shoulder, doubled in Roberts.
Shawn Hill (0-1) took the loss, giving up five runs on eight hits in five innings. The Nationals had won their two previous games.
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