BOSTON — Mark Loretta’s All-Star buzz didn’t last very long.

The Red Sox second baseman missed Bobby Kielty’s easy grounder and allowed an unearned, game-tying run to score on Thursday night as the Oakland Athletics rallied to send the game into extra innings and beat Boston 5-4 in the 11th.

“I took my eye off it and it was gone,” said Loretta, who made his first All-Star start on Tuesday night thanks to a first half in which he committed just three of the team’s major league-leading 30 errors. “It was more a mental lapse than anything.”

Kielty singled to score Jason Kendall and break an 11th-inning tie, then stole second and scored on Frank Thomas’ single to make it 5-3. Jason Varitek’s RBI single in the bottom of the inning made it Oakland’s league-leading 18th one-run victory of the season.

“Every day is a one-run game,” A’s manager Ken Macha said. “It seems that way, at least.”

Huston Street (3-3) pitched 12/3 innings, striking out two, for the win. Kirk Saarloos, who is supposed to start on Monday, got the last two outs for his second save; he was the eighth Oakland pitcher in the game.

“After you get three days off, you like to get guys back into the game to get their feet wet,” Macha said.

“We basically did that in one game.”

It was Boston’s first home loss in 10 games since June 11. The Red Sox left at least one runner on base in 10 of the 11 innings.

The Red Sox, who played 19 innings in their last game before the All-Star break, led 1-0 and 3-1, but two runs scored — one unearned — on Loretta’s seventh-inning error.

It stayed 3-3 until the 11th, when Kendall doubled with one out and Nick Swisher, who homered in the third, struck out on a close-call checked swing.

Kielty hit a hard liner off the scoreboard of the Green Monster, and Kendall scored easily.

Thomas added the insurance run against Julian Taveras (1-3), who worked one inning, allowing three hits and two runs.

Oakland had lost four of five and seven of its previous 10 games.

Boston rookie Jon Lester pitched five laborious innings, needing 103 pitches to qualify for what would have been his fifth consecutive victory.

He allowed one run, five hits and five walks while striking out three before leaving with a 3-1 lead.

Craig Hansen pitched a perfect sixth but gave up singles to Antonio Perez and Kendall to lead off the seventh.

Manny Delcarmen came on with one out and runners on second and third and got Kielty to hit an easy grounder to second, where Loretta took his eye off the ball and it went by him for an error.

Perez and Kendall scored — the latter run was unearned — to make it 3-3.

David Ortiz was 2-for-4 with two walks. He doubled to lead off the third and scored on Trot Nixon’s single to give Boston a 2-1 lead. Varitek singled and Mike Lowell, who hit a solo homer in the second, added an RBI fielder’s choice to make it 3-1.

After the game, the A’s activated OF Milton Bradley from the 15-day DL and optioned 1B Dan Johnson to Triple-A Sacramento.