Machado's solo blast against Bosox starter Felix Doubront (11-10) broke a 3-3 deadlock and carried the Orioles to their third straight victory.
Coupled with the New York Yankees' loss to Toronto Saturday, the Baltimore pulled into a first-place tie atop the American League East with four games remaining in the regular season.
Chris Davis cracked a two-run homer for Baltimore.
Doubront allowed four runs (three earned) on seven hits over seven innings, striking out 10.
Jarrod Saltalamacchia supplied a two-run shot for Boston.
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UPI Sports Results for September 19, 2014