Jon Lester tossed seven scoreless innings, while David Ortiz finished 4-for-4 with a two-run homer, as Boston silenced Baltimore, 5-0, in the rubber match of a three-game series.
Lester (10-6) scattered four hits and walked two with eight strikeouts, throwing 99 pitches, 65 for strikes. Matt Thornton and Pedro Beato followed with scoreless frames to lock up the contest.
"Outstanding effort on his part," Red Sox manager John Farrell said of Lester. "He pitched us to a series win which has been a while since he have been able to win more than we lose in a series against the Orioles."
Jarrod Saltalamacchia drove in a pair, while Mike Napoli doubled twice and knocked in one for the Red Sox, who moved a half-game ahead of Tampa Bay for the AL East lead. The Rays lost to the Yankees on Sunday.
Jason Hammel (7-8) lasted 5 1/3 frames, charged with six hits and three runs, walking five but fanning only three for the Orioles, who dropped the final two in the set.
"We're grinding right now, not going too hot," Hammel admitted. "We're still playing close ball games. It's not like we're getting blown out."
The Sox picked up a run in the first. Shane Victorino walked with one out, went to third on a two-out hit from Ortiz and scored when Napoli followed with a double.
In the third, Jacoby Ellsbury led off with a base hit and came in when Ortiz clobbered a two-out shot to left for a 3-0 game.
Ortiz singled and Napoli doubled with one down in the eighth, and both crossed the plate on Saltalamacchia's one-out single to give the BoSox a five-run advantage.
Lester retired 11 in a row from the first until a two-out single from Adam Jones in the fourth. Matt Wieters walked, but J.J. Hardy fouled out to end the threat.
Manny Machado lined out to complete the fifth with two on, then Lester induced an inning-ending double-play grounder from Hardy with two aboard in the sixth.
Baltimore went quietly in Lester's final inning of work, and a Nick Markakis single in the eighth was the bullpen's lone blemish in the last two frames.
Lester improved to 4-2 in his last seven outings since June 21, upping his career mark against Baltimore to 15-2 in 23 career starts and halting a two- decision losing streak against the O's after beginning his career with 14 victories ... Boston's Sunday victory ended a streak of six straight series losses to the Orioles dating back to Sept. 19, 2011 ... Ortiz collected his 20th home run, the 12th consecutive season he's reached the plateau.