Lester (10-6) scattered four hits and walked two while striking out eight in the 99-pitch performance, winning a second straight start.
Mike Napoli also provided an RBI for the Bosox, who bypassed Tampa Bay for the top spot in the American League East following the Rays' Sunday loss to the New York Yankees.
Jason Hammel (7-8) was touched for three runs on six hits over 5 1/3 innings for third-place Baltimore, which fell five games off the pace in the AL East.
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