Lester, back after a one-start return to the Minor Leagues, earned the win by limiting the Orioles to six hits and two runs over six-plus innings.
"It's kind of an exciting day when we can send out some young kids right in the middle of a pennant race and be excited about it," said Red Sox manager Terry Francona. "Their impact of the game was everywhere. That's a really good feeling. Sometimes you get in positions where guys are beat up and you're playing people. But when you've got young guys coming up and you're excited about them helping you win, that's a good feeling."
Brandon Moss, yet another callup, also made his presence felt. Making the start in place of the injured Manny Ramirez, Moss rammed into the Green Monster to make a nice catch.
"It's been fun to watch," said Red Sox general manager Theo Epstein. "We've talked for a few years now about how our biggest organizational challenge is to develop players who can come up in the middle of a pennant race and contribute. I think we saw that happen a little bit this weekend. It's a credit to our scouting and player-development staff and to our Major League staff to have the right touch with these guys and seamlessly integrate them into the big league club."
Not that it was all about the youth movement. J.D. Drew made a tremendous throw from right field for an inning-ending double play in the fourth. Mike Lowell, Mr. Reliability, drove in two more runs to give him 97 RBIs for the season.
The Orioles made a strong comeback bid from after being down, 3-0, and had a chance to tie the game in the top of the eighth after putting a runner at third with one out. But Hideki Okajima got himself out of that jam by striking out Kevin Millar and Aubrey Huff.
Jonathan Papelbon effortlessly put away the Orioles in the ninth for save No. 31.
With the win, the 82-55 Red Sox boosted their lead over the Yankees back to six games in the American League East with 25 games to go.
"I didn't want us to have a letdown because of how exciting everything was last night, and I think Jon did a good job," said Lowell. "He gave us a quality start. We were able to hold on to a lead. Oki did a great job in the eighth. It was a good win. Lose the first game, come back and win the series, that's a good job."
The Red Sox broke out first against Orioles starter Daniel Cabrera when Lowell belted an RBI single to left in the bottom of the first, extending his hit streak to 15 games. They got another jolt when Ellsbury put one into the Boston bullpen in right-center for a solo shot.
"It was very exciting," Ellsbury said. "You know, I wasn't really trying to do too much with it, just try to hit it where it's pitched and hit it hard. ... He left a changeup up in the zone, and I was just hoping [Nick] Markakis wasn't going to catch it.
While Ellsbury's ability to hit for contact and blaze around the bases and center field are well-known, his power is his biggest unknown.
"Right after we signed him, we brought him in here with wood and he was launching balls over our bullpen," Epstein said. "I don't think we have any questions about his raw power. I think, as he learns his swing and as he continues to develop, he's going to figure out how to backspin the ball more consistently. When he does, he has much more raw power than you would think from his frame."
While O's Cabrera was holding his own, the Red Sox were doing just enough to maintain the lead. Dustin Pedroia led off the fifth with a double to left and Alex Cora sacrificed him to third. That put Lowell in position to loft a sac fly to left.
Aided by some strong defense, Lester had a shutout after five.
The Orioles got one back in the sixth on Melvin Mora's RBI single to left. Ramon Hernandez led off the seventh with a homer into the Monster seats, and that was all for Lester, who picked up the win to improve to 3-0.
"It felt good," said Lester, "a lot better than my last couple of starts. When I was in Portland, I started to figure some things out consistency-wise and where my body is, where my arm was at. ... At times today, I felt really, really good."
Lester had plenty of familiar company on the field with him in this one.
"We've come up through the system together," said Lester. "We know what we can do and we push each other. Jacoby made some great plays out in center today as did Moss. You know, [Pedroia] made some plays up the middle. The defense played really well, and it's fun to see those guys up here."