Through five innings, Lester piled up 10 strikeouts -- allowing just one walk and one hit, a leadoff single by Craig Gentry in third. Lester dominated the A's over his eight scoreless innings, giving up just Gentry's hit, two walks and compiling a career-high 15 strikeouts.
"Just the combination of power and command was impressive," said Red Sox manager John Farrell. "He was locked in seemingly from the first pitch of the game. He maintained his stuff throughout -- four pitches for strikes, and three of those on both sides of the plate. So he was in command from the start."
It was Lester's 18th career game with double-digit strikeouts, tying him with Smoky Joe Wood for third on the Sox's all-time list, behind Pedro Martinez (72) and Roger Clemens (68).
"Anytime you mention those two names, it's pretty special," Lester said. "Obviously, not one of those deals you focus on or worry about or anything like that. [It] just kind of happened today. It's an honor to be in [the same conversation] with those guys' names. Hopefully, [I'll] get another day like this someday."
Lester had at least one strikeout in every inning but the seventh. He had three strikeouts in the third and the eighth, both after allowing the leadoff batter to reach base. Seven strikeouts came via his cutter. But, he couldn't tell from warming up in the bullpen if the pitch would behave for him.
"[My] cutter was backing up. That was probably the worst cutter I've thrown in the bullpen in a long time," said Lester. "I don't take much stock in my bullpens anymore. You're down there to get loose. I think the biggest thing for me is getting on that mound and getting that adrenaline going -- and that tempo with my delivery and [getting] my arm out of my glove."
He did that, earning the win to improve to 3-4, while lowering his ERA from 3.10 to 2.59.
David Ross was behind the plate for Lester.
"That was a lot of fun," Ross said. "That was. I mean, when a guy is doing what he was going today, it's fun to be a catcher. Just moving the ball in and out, he was a lot of fun to catch."
Lester was not a lot of fun to face, though.
"He had command of that cutter, he had command of that fastball. Curveball, he kept us off-balance with it. For the most part, he was just spotting up with that fastball and cutter," said Nick Punto, Lester's teammate with the Sox in 2012, who struck out twice against him on Saturday.
"That's the best performance I've seen him have. He didn't miss too many spots today all day long against very many hitters.
"He just looked like he's pitching with a lot of confidence out there. He's always been a stuff guy, a guy with really good stuff. It looks like he's putting it all together."
Meanwhile, Boston's offense made a dominant statement of its own. In the first inning, Dustin Pedroia led off with a walk against Oakland lefty Tommy Milone, followed by Xander Bogaerts single, and a walk to David Ortiz before Mike Napoli struck out swinging at an 87-mph fastball.
Jonny Gomes followed by jumping on Milone's first pitch, a 76-mph curveball, and crushing it into the Monster seats in left field for the Sox's second grand slam in as many days against the A's. It was the first time the A's have given up grand slams on consecutive days since Sept. 25-26, 1999, to the Rangers.
After Gomes' slam, Milone seemed to settle down. He retired the next four batters -- all on strikeouts -- giving him K's on his first five outs. But the Sox would strike again.
The Red Sox scored all six of their runs via home runs, as Ortiz led off the third and Ross led off the fourth with solo shots. Ortiz's home run was his 379th with the Red Sox, tying him with Dwight Evans for fourth place on the team's all-time list.
Boston knocked Milone from the game in the fifth, after he walked Napoli, giving way to right-hander Dan Otero. In a season-low four-plus innings, Milone allowed a season-high six runs on six hits, while tying a season-high with four walks, and recording five strikeouts. Entering the game, he had allowed just one home run over four starts spanning 23 2/3 innings, and that came in his first outing on April 11 at Seattle.
"He just got behind early, and he just gets into a position where he's got nowhere to go with Gomes and just hangs him a curveball on the first pitch," said A's manager Bob Melvin. "Just couldn't get off to a good enough start to limit the damage."
Oakland mounted a late challenge in the ninth, scoring three runs off Chris Capuano. But closer Koji Uehara managed to nail down his seventh save.
Milone took the loss, falling to 0-3, as his ERA climbed from 4.56 to 5.86.