Lester (7-2) allowed four hits and three walks while fanning four to improve to 11-0 lifetime against the Orioles, as the Red Sox notched their seventh straight road win -- the longest such streak for the team since 2005. Lester also won his fourth straight start and has won seven straight decisions over his last nine trips to the mound.
Baltimore's Jeremy Guthrie (3-6) was dealt the hard-luck loss after giving up just two runs on five hits and a walk in 7 1/3 frames. Despite the loss, Guthrie has given up just nine runs over his last five starts, spanning 33 1/3 innings.
The Orioles' losing streak reached 10 games, during which they've scored only 16 runs. Scott Moore hit a two-run single in the ninth for Baltimore to snap a 19-inning scoreless stretch.
The Red Sox looked to get on the board right away, putting runners on second and third with two out, but Victor Martinez struck out to end the threat.
The Orioles threatened again in the fifth, as runners reached second and third with just one out. Lester, though, recovered to retire Cesar Izturis on a pop out before inducing a ground out from Patterson to keep the game scoreless.
Leading off the seventh, Youkilis sent the first pitch he saw to the seats in left to break the tie and give the Red Sox the lead.
Lester got into some trouble in the seventh, issuing three consecutive walks with one away. Daniel Bard came in and got pinch-hitter Luke Scott to fly out to shallow center and Patterson to foul out to maintain Boston's advantage.
"I felt good early on, got in a rhythm, threw strikes," Lester said. "In the seventh inning, I don't know if it was the heat or a lot of pitches or what, but it just kind of caught up to me a little bit. The bullpen did a good job bailing me out right there."
The Red Sox added some insurance in the eighth. Josh Reddick, called up from Triple-A earlier in the day, tripled to the gap in right-center, and Marco Scutaro singled over the drawn-in infield two batters later to plate Reddick for a 2-0 lead.
"The game was very close, we fought Lester, it could have gone either way that particular inning there," Orioles interim manager Juan Samuel said of the seventh frame. "Those guys are not thinking, they're not looking at their record of Lester against us."
Boston padded its advantage in ninth. Three walks loaded the bases with one out, and McDonald sent a bloop double down the left field line to plate two runners. Hall followed with another double to left to score two more for a 6-0 cushion.
Youkilis added another two-run double later in the inning to put the Red Sox ahead by eight.
Moore hit a two-run single for the Orioles in the final frame to account for the final margin.
The season series is tied, 4-4...Guthrie fell to 1-6 in his career against the Red Sox...Baltimore has a 6-23 record in the AL East...Youkilis finished with three hits...To make room for Reddick, Boston optioned pitcher Scott Atchison to Triple-A Pawtucket.