BOSTON -- Dustin Pedroia was trying to be the face of confidence standing in the middle of a very quiet Red Sox clubhouse.

"We've got the lead. We've just got to go out and play better. We're not hanging our heads," he said after fading Boston lost for the 12th time in 15 games, dropping the opener of a day-night doubleheader 6-5 to the Baltimore Orioles on Monday.

Jeremy Guthrie (9-17) pitched the last-place Orioles to the win, cutting Boston's once-large AL wild-card lead to 1½ games over charging Tampa Bay.

Boston rallied from a 6-2 deficit and cut the lead to two when a missed call cost the Red Sox a run and halted their comeback bid.

TV replays appeared to show that David Ortiz's fifth-inning liner down the right-field line -- ruled foul by first-base umpire Mike Estabrook -- seemed to carom fair off the lower part of a short wall near the Pesky Pole with Pedroia on third after an RBI triple.

"That's the breaks of the game," Pedroia said. "We've played a hundred-something games. We're not going to say the season's over because an umpire missed a call."

Boston, which lost three of four games against Tampa Bay this past weekend, led the Rays by nine on Sept 3. The Red Sox have dropped 15 of 20 since they held a 1½-game edge over New York atop the AL East on Aug. 30.

The Yankees now lead the division by 5½ games.

"Any loss hurts," Boston manager Terry Francona said. "We battled, and battled and battled and came up short. I'm glad we're playing again right away."

The Red Sox have six games remaining against Baltimore and three in New York against the Yankees. The Rays have 10 to play.

Robert Andino hit a two-run homer and Nolan Reimold followed with his 12th, putting the Orioles ahead 5-1 in the fourth. J.J. Hardy led off the fifth with his career-high 28th home run.

Baltimore won for the first time in six games at Fenway Park this year, getting outscored 40-20 in the five loses.

"These are some pressure games. I want to see those guys in those situations," Orioles manager Buck Showalter said. "Hopefully down the road they'll be pitching in games that mean a little bit more for us."

Guthrie pitched into the seventh inning for his first career win in Fenway Park. He had been 0-3 and the Orioles had lost all seven of his previous starts.