BOSTON – Jon Lester threw a quality start.

That sounds nice when we’re talking about Felix Doubront, a young pitcher still trying to consistently command his pitches.

But Lester is the Red Sox ace. And he took the loss Thursday night in a 3-2 defeat to the Baltimore Orioles.

Whether Lester is the ace later on — later, as in October, if Boston is still playing — is another question.

A quality start is generously classified as an outing of at least six innings and no more than three earned runs. That’s good for a 4.50 ERA (which would rank around 71st among major league starters.

Nice, but hardly ace material.

Lester, now 12-8 with a 3.99 ERA, has been teasingly close to flashing his dominating self. He shut out these Orioles over seven innings on July 28, only to give up six runs to Arizona in his next start.

On the Red Sox successful West Coast trip, Lester allowed one run over 152/3 innings in two wins.

“It all centers around his fastball command,” Boston Manager John Farrell said of Lester’s success.

That command escaped him at times Thursday. His pitch count rose, and he missed on pitches, like the 0-2 fastball he left up to Chris Davis, whose two-out RBI double in the fifth was the game-winner.

Lester limited the damage. He got a quality start. But Boston is going to need more from its ace.

RYAN FLAHERTY doubled in four at-bats, but he was not at Fenway Park. Flaherty was in Maryland, playing second base and batting third for the Delmarva Shorebirds of the South Atlantic League.

Flaherty, 27, the Portland native and Orioles utility player, was sent down to the minors on Tuesday to make room for switching-hitting infielder Wilson Betemit, who was coming off the 60-day disabled list.

Rosters can be expanded Sunday and Flaherty is expected to rejoin the major league team soon after that.

Flaherty, who bats left-handed, was not likely to be playing a lot, anyway, not with the Orioles facing lefties Felix Doubront (this past Tuesday), Lester, and CC Sabathia tonight.

CLAY BUCHHOLZ is scheduled to start tonight for Triple-A Pawtucket in his second rehab start.

Farrell said Buchholz would make a third rehab start next week, likely with Pawtucket (assuming the PawSox are in the playoffs, and they are close to clinching a spot).

Ideally, Farrell said, Buchholz would stay in the minors even longer. But because the rosters expand in September — and the Red Sox will have a bullpen busting at the seams — Buchholz can be called up, even he can go only four or five innings.

“He’s going on three months missed and you might say three (rehab) starts is short,” Farrell said. “But given the time of the year, we’re covered.”

Buchholz could be back on Sept. 10. Good timing. That’s the first game of the final series against the Tampa Bay Rays.

SPEAKING OF THAT Red Sox bullpen, it’s a little left-handed heavy, with Craig Breslow, Drake Britton, Franklin Morales and Matt Thornton.

Might the Red Sox look for one more right-handed reliever before Aug. 31?

“If there is someone who makes sense for us to acquire, we might see that,” Farrell teased.

DANIEL BARD IS not likely to be considered a right-handed boost to the bullpen.

Bard, who was shut down in May when he was with the Sea Dogs, made his first appearance last Monday, pitching in the rookie Gulf Coast League.

Farrell said Bard’s “velocity isn’t where it was when he was (in Boston) for a brief time or in spring training. The fact that he’s on the mound is one step.”

Farrell did not rule out Bard returning this year but that seems doubtful, especially after his appearance Thursday in the Gulf Coast League. Bard faced six batters. One flied out. The other five walked.

MATT BARNES may be in the major league conversation next year. He made his Pawtucket debut Thursday and pitched 5 1/3 scoreless innings, allowing three hits and two walks, while striking out seven.

Barnes, just promoted from the Sea Dogs, retired the first batter in the sixth and was then relieved. He threw 86 pitches, 56 for strikes.

RYAN DEMPSTER might be considered a bullpen option. Assuming Buchholz comes back healthy, Dempster is likely the odd pitcher out of the rotation.

Dempster, who served a five-game suspension for beaning Alex Rodriguez on Aug. 18, and then was given a few more days off, gets the start tonight for Boston, when the White Sox come to town.

“He’s rested, I know that,” Farrell said.

Kevin Thomas can be reached at 791-6411 or:

[email protected]

Twitter: ClearTheBases

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