The win, coupled with the Yankees' 6-4 loss to the Athletics on Saturday afternoon, pulled the Sox within 1 1/2 games of New York in the American League East.
Boston's recent struggles at the plate, which came to a head during its 1-5 road trip following the All-Star break, never crept into Lester's mind. The left-handed workhorse yielded two runs on eight hits over 7 1/3 innings, striking out nine.
Lester has allowed three runs or fewer in each of his past 10 starts, a sterling streak that began on May 31. Over that span, he's averaged 10.96 strikeouts per nine innings.
Saturday's performance, however, didn't come without some adversity.
"My bullpen wasn't the best bullpen I've ever thrown," said Lester, who improved to 9-7 overall. "But I just tried to take the mentality of getting loose and getting ready to play a game. I was able to go out and get ahead early. When I'm able to throw well and throw strikes early on, it makes the game that much easier."
Making his Red Sox debut, LaRoche followed up three hitless at-bats by swatting his first American League home run in the eighth, a two-run blast over the Green Monster that put the game out of reach.
"I felt pretty good in my first at-bat," said LaRoche, who finished 1-for-4. "Then I felt a little antsy and a little jumpy, but after that, I felt really good. I just missed some pitches. I was hoping I could get that first one out of the way sooner than later."
"I know he hasn't played here much," manager Terry Francona said, "but he has that Fenway swing. That should breed some confidence."
The left-handed slugger was all smiles after experiencing the high-voltage Fenway atmosphere for the first time in a home uniform.
"It's a huge difference," LaRoche said, referring to his former baseball home in Pittsburgh. "I felt like I was in the playoffs. I'm jealous that these guys got to do this every night before I got here. If you can't find energy here, there's something wrong with you."
Facing a pitcher in Baltimore starter Jeremy Guthrie (7-9) who entered Saturday tied for the American League lead with 22 home runs allowed, Ortiz greeted the right-hander in the first by tattooing a 1-0 pitch over the center-field wall for a three-run shot.
"Getting those three runs in the first inning kind of loosened us up a little bit," Ellsbury said. "It just let us swing the bats freely."
The speedy center fielder extended the Red Sox's lead to 4-0 one inning later, lofting a double over the head of Adam Jones in center to score Jason Varitek.
Baltimore (41-55) touched up Lester for a pair of runs in the fourth, as RBI singles from Matt Wieters and Cesar Izturis pulled the Orioles within two.
Boston plated an insurance run in the bottom of the frame, when Ellsbury delivered Nick Green with a well-struck double into the right-field corner.
Removed from their worst road trip of the season, which included a forfeiture of first place in the AL East, the Red Sox have suddenly returned to their winning ways, thanks to some home cooking.
"I think everybody was happy to get off that road trip," Ellsbury said. "It definitely wasn't one of our better road trips, but coming home, with our fans, has really worked out for us."
"We need to produce," Ortiz said. "That's the only way you're going to win games. With New York playing well, we need it. We've got to bring it."