For the first time in franchise history, the Orioles have won seven consecutive games in Boston.
Chen (5-2) allowed a run over seven innings without a walk. His top prior outing in his rookie season occurred last month against the New York Yankees, when he gave up up two runs.
The lone score off Chen came on a third-inning sacrifice fly from Mike Aviles.
Chen outdueled Josh Beckett (4-6), who surrendered both Baltimore runs on five hits with no walks in eight innings. Beckett has lasted at least seven innings in each of his last five outings.
Baltimore scored twice in the sixth, with Wilson Betemit, Ryan Flaherty and Robert Andino all delivering singles to open the inning. Betemit scored on Andino's base hit and Flaherty came in on a fielder's choice grounder by Endy Chavez.
Jim Johnson retired the side in order in the ninth for his 18th save.