The victory catapulted the Orioles (86-64) atop the American League Wild Card standings and also keeps them just one game back of the AL East-leading Yankees.
"Jon was good actually tonight," manager Bobby Valentine said. "His pitches were crisp. He battled the whole way. We got a one-run lead for him and then tied it up and just couldn't get that inning to get the guys back in the dugout, maybe feeling good about ourselves."
For three innings, at least, Lester had it going. He fanned Nate McLouth with a high-and-tight cutter in the game's first at-bat and didn't let a runner touch second base until Robert Andino ran over it once, turned back around and darted back the other way late in the third.
While Andino was sprinting the bases, Ross made a leaping catch against the right-field wall and immediately hurled a throw toward the infield. By the time Andino turned around and started jetting back to first, it was too late, as Dustin Pedroia hooked up with James Loney for an outfield-assisted double play.
It wouldn't be the last time Lester was bailed out by spectacular defense.
After leadoff hitter Pedro Ciriaco doubled in Daniel Nava to give the Sox a 1-0 lead in the bottom of the third, the Orioles came back attacking the following inning.
J.J. Hardy, Adam Jones and Matt Wieters all connected off Lester's pitches to plate a pair of runs. Still fighting with one out, 20-year-old phenom Manny Machado smacked a pitch back toward the mound and fed Lester an easy double play.
But Lester couldn't make the short toss to second.
Iglesias stabbed the ball out of the dirt and quickly touched the bag before slinging a bullet over to first base just in time to nail Machado, but not in time to avoid Lew Ford's sliding cleats.
"Iggy made a couple of good plays," Lester said. "Pedro made a good play. That's nice to have, especially on those tough balls. You feel like you made a good pitch, and a guy makes a great play."
In the midst of an 0-for-18 slump, Pedroia had the opportunity to tie the game in the fifth.
Miguel Gonzalez threw seven pitches and Pedroia fouled off three of them, benefited from some questionable, may-have-earned-it umpiring from Mark Wegner behind the plate and willed a base hit through the left side of the infield to score Ciriaco.
The game was tied at 2, and Lester trotted back to the mound for the top of the sixth inning ready to thrive off Pedroia's delivery.
Lester took care of the first batter, getting a ground ball to retire Hardy at first. The southpaw then wanted no part of Jones, giving him a free base on five pitches.
Wieters must have been laughing in the on-deck circle.
Wieters stepped up and took a half-swing at a fastball, slapping one just wide of Pesky's Pole. On the next pitch, Wieters crushed a double to the left-field corner and Jones scored easily.
"Even the couple of balls to Wieters, they were fine," Lester said. "They were where I was trying to go with them. ... I've just got to keep trying to execute the pitch. The process was there. The intent was there. The game plan was there. It just didn't work."
Lester couldn't bounce back.
He sailed a pitch over Ryan Lavarnway's head with Mark Reynolds in the box, letting the slow-footed Wieters walk to third. Reynolds then proceeded to loop a base hit over the drawn-in infield to score Wieters and add to the lead.
For Reynolds, hitting .231 on the year, it was just his 48th single in 411 at-bats this season. And it buried Lester.
Valentine said that Lester has just been unlucky, and it's been hard for the lefty because the Sox haven't been putting up double-digit runs during his starts, forcing Lester to make every pitch "a crucial pitch."
"If he pitches like that, the way he's pitched the last couple of months, even the whole second half, he's going to win a lot of games," said Valentine.
Lester is 4-7 with a 5.60 ERA in the second half compared to 5-6 with a 4.49 ERA prior to the All-Star break.
"He's been tough against us," Wieters said. "All year, all prior years ... but we were able to get a few runs off him today."