John Lackey put together a solid outing — seven innings, two earned runs and two strikeouts — but the Red Sox left the bases loaded in the sixth and seventh.
Mike Cameron took over late with a potentially game-saving catch and the game-tying run in the ninth.
But with the game still tied at three in the 11th, a Markakis bloop single did in the Red Sox.
End 11th, 4-3 Orioles: The O's walk-off with a win to salvage the last game of the series.
Izturis walked to lead off the inning. Lugo sacrificed to first, putting Izturis in scoring position.
With first base empty, Tito opted to give Miguel Tejada an intentional pass.
Then Markakis blooped one that dropped in shallow center. Cameron had little chance of cutting down the speedy Izturis, who stepped over Varitek for the game-winner.
Mid 11th, 3-3: McDonald makes it to second base, but the Red Sox can't push him across the plate.
With one out, McDonald laced one toward third that looked headed for extra bases. The third baseman Moore lunged to his right to make a great stop, but McDonald motored down the line to beat it out anyway.
A wild pitch by Hernandez advanced McDonald to second, but Scutaro and Pedroia couldn't get anything going to leave him stranded.
End 10th, 3-3: Okajima registered the Sox' first one, two, three inning of the game on a foul out and a pair of fly outs.
Okajima needed just eight pitches to take care of the O's.
Mid 10th, 3-3: Youkilis was hit by a pitch to lead off the inning, but David Hernandez set the Red Sox down in order after that.
J.D. Drew pinch-hit for Bill Hall, ending the inning with a fly out to right. He'll enter the game in right field, and McDonald will move to left.
Hideki Okajima will take the mound for the Sox.
End 9th, 3-3: Cameron did his best Willie Mays impression to keep the game alive.
Jonathon Papelbon came on to retire the first two batters, before a nine-pitch battle with Wigginton led to a two-out walk.
Then Lou Montanez put a charge into one the looked bound for extra bases. But Cameron got a good jump and sprinted with his back to the plate, cradling the big fly over his left shoulder just short of the warning track.
Wigginton was rounding second as Cameron hauled it in.
Will we see Papelbon out for another one if the Sox score in the 10th?
Mid 9th, 3-3: Cameron was the catalyst for a Red Sox offense that had stranded runners all day.
After singling to start off the inning, he advanced to second on a sacrifice bunt by McDonald.
Then the veteran centerfielder exhibited smart baserunning on a single by Scutaro, seeing it through the hole before breaking for third.
Pedroia skied one to center to score Cameron, and Will Ohman notched the blown save.
End 8th, 3-2: Manny Delcarmen missed high for much of the inning, but it was a low breaking ball that Scott Moore doubled into the right field corner to score the go-ahead run.
Delcarmen left the game after walking the next batter, Tatum. All indications point to back problems as the culprit.
Ramon Ramirez came on to draw back-to-back flyouts to Cameron in center.
Mid 8th, 2-2: Victor Martinez led the the inning off with a single. But Adrian Beltre grounded into a double play to clear the bases, and Bill Hall struck out swinging.
Josh Reddick ran for V-Mart, and Jason Varitek has come on to replace him.
End 7th, 2-2: Marco Scutaro made a nice play in the hole to strand two runners and keep the score tied.
Pedroia ranged to his right and bobbled a slow grounder, allowing Izturis to reach to begin the inning. A Lugo sacrifice bunt advanced the runner to second, and one out later, Markakis walked to put runners on first and second. Wigginton grounded to Scutaro, who threw on to second to end the inning.
Lackey threw his season-high 124th pitch of the day.
Mid 7th, 2-2: Two pitching changes and two walks later, the Red Sox are still tied with the O's.
Scutaro and Cameron reached on free passes from Albers, who was pulled with two outs and runners on first and second.
Mark Hendrickson came on to face Big Papi, and hit the slugger with a pitch. Then the O's went to Jason Berken, who drew a harmless flyout from Youkilis to end the inning.
The Red Sox have left the bases loaded in each of the past two innings.
End 6th, 2-2: Adam Jones singled, but Lackey looked good again in the 6th.
Lackey has yet to retire Baltimore in order, but he is through six with just two blemishes on his record.
The rain picks up at Camden Yards.
Mid 6th, 2-2: The Red Sox sent Matusz to the showers, but didn't come up with any runs to show for it.
Pedroia beat out an infield single to the pitcher to lead-off the inning. When Big Papi struck out swinging, Pedroia swiped second on a throw that skipped short of second base. Then Youkilis flied out.
With first base empty, the O's intentionally walked Martinez to get to Beltre, who's hitting .423 against lefties. Matusz walked Beltre and the O's yanked the youngster in favor of Matt Albers.
Albers got Hall to ground out to the shortstop, leaving the bases loaded.
End 5th, 2-2: The O's went quietly in the 5th. After sending down the first two batters, Lackey walked Markakis in a five-pitch at-bat. But the righty jammed Wigginton on an inside fastball, forcing a lazy pop up that Scutaro camped under to retire the side.
Mid 5th, 2-2: Mike Cameron walked to put a runner on first with one out. But the Sox couldn't advance him, as Marco Scutaro lined out softly to the shortstop to close the frame.
End 4th, 2-2: Craig Tatum singled, but Lackey coaxed a 6-4-3 double play from Cesar Izturis to get out of the inning.
Mid 4th, 2-2: Big Papi remains hitless in the series thanks to a fly out to right-center.
Youk extended his hitting streak to six games with an infield single to third. The swinging bunt down the line was bobbled by Moore as he sprinted in for the bare-handed attempt.
Matusz got back-to-back strikeouts once again to end the frame and has five on the afternoon already.
End 3rd, 2-2: Lackey was able to shake off a rough second inning as he got a pair of ground-ball outs to start the bottom of the third. Luke Scott, who doubled already off Lackey, roped a harmless single to right as Jones followed him with an inning-ending ground out to third.
Mid 3rd, 2-2: Matusz got the O's bats back into the dugout as the lefty worked a 1-2-3 third inning.
McDonald, Scutaro and Pedroia were each retired by fly-ball outs.
End 2nd, 2-2: After giving up a leadoff double off the left-center fence to Luke Scott, Lackey struck out Adam Jones for the inning's first out.
But after that, things got ugly for the big righty.
Scott Moore started things off by grounding one into the hole between third and short, which Scutaro made a fine play to get to, but the weak off-balance throw across his body was too late.
Although the runners failed to advance on the poor throw and remained at first and third, Youk probably could have come off the bag to make sure the ball stayed in the diamond. Then again, he's a Gold Glover, so what do I know?
Lackey loaded the bases by walking Tatum and the next batter, Izturis, roped an RBI-single up the middle to plate the O's first run. Lugo then chopped into a fielder's choice and due to the slow underhand flip by Scutaro to Pedie at the pivot, the Sox were unable to complete the double play, allowing the tying run to score.
Mid 2nd, 2-0, Red Sox: Martinez smacked a high heater over the left field fence with Youkillis aboard to put the Sox up 2-0.
It's V-Mart's eighth of the season and first of the month and his 28th and 29th RBIs. The catcher has now scored at least one run in five straight games. In that span, he also has five RBIs, four doubles and is batting .611 (11-for-18) to go with just two strikeouts.
Bill Hall bounced into a double play after an Adrian Beltre single and Mike Cameron ended the frame with a strike out.
End 1st, 0-0: Lackey kept the O's off the board in the first as the righty struck out Julio Lugo to begin things.
Although Tejada roped one down the third-base line for a one-out double, the hurler got Markakis and Wigginton to fly out.
Mid 1st, 0-0: Matusz looked strong in the first frame as he struck out both Dustin Pedroia and David Ortiz in order to end it.
The Fenway South crowd is very thin for this afternoon's contest. Hopefully the Nation is just a little late to the park because of excessive celebrating after Saturday night's win.
12:24 p.m.: Cameron is penciled in at center and will bat eighth for his first game since last Sunday.
Also returning is third baseman Adrian Beltre, who sat out Saturday night's 8-2 win.
Red Sox
Marco Scutaro, SS
Dustin Pedroia, 2B
David Ortiz, DH
Kevin Youkilis, 1B
Victor Martinez, C
Adrian Beltre, 3B
Bill Hall, LF
Mike Cameron, CF
Darnell McDonald, RF
Orioles
Julio Lugo, 2B
Miguel Tejada, DH
Nick Markakis, RF
Ty Wigginton, 1B
Luke Scott, LF
Adam Jones, CF
Scott Moore, 3B
Craig Tatum, C
Cesar Izturis, SS
10 a.m.: All signs are pointing to Mike Cameron starting in center field for Sunday's matinee match.
"If he’s OK [Sunday], he’s going to play," Francona said on Saturday.
The outfielder has been out since last Sunday due to soreness in his left side.
8 a.m.: The Sox send John Lackey to the hill as the squad seeks a weekend sweep over the lowly Orioles in Baltimore.
Boston has outscored the O's 19-2 in the first two contests of the three-game set and will hope to keep their bats warm for the Sunday afternoon contest that kicks off at 1:35 p.m. on NESN.
Lackey is at 6-3 with a 4.95 ERA in 11 starts this season with the Sox. He's 9-3 with a 3.17 ERA in 14 career starts against the O's and bag his third straight win.
Facing to Sox will be Brian Matusz who is at 2-6 with a 5.28 ERA in just his second big league season. The lefty faced to Sox earlier this season, when he gave up six hits and three runs over six innings for the no decision.
