"I don't think I had my curveball to put guys away," he said. "It was difficult for me to get the ball down, particularly bouncing the breaking ball."
Jarrod Saltalamacchia kept up his torrid hitting of late, but the rest of the Red Sox's offense didn't muster much against Tigers starter Max Scherzer and Detroit's bullpen.
The Red Sox had seven hits through the first four innings, but they managed only one baserunner after that.
"We just let [Scherzer] off the hook," said manager Bobby Valentine. "We had his pitch count up in the 80s after four innings and we were having good at-bats. We just let it slip away."
Saltalamacchia homered to lead off the second inning, launching a 1-1 pitch over the Red Sox's bullpen in right. He added an RBI single in the third that scored Kevin Youkilis and finished the night 2-for-4.
The catcher has six homers in his last 16 games, a career high for a single month. Over that stretch, Saltalamacchia is hitting .373 (19-for-51) with 14 RBIs and four doubles.
But he had a pair of throwing errors attempting to catch runners stealing second and both led to runs, including the go-ahead run in the fifth inning and another in the ninth.
"The last one he didn't get a good grip on it," Valentine said. "I thought Mike [Aviles] was a little late getting there."
The Tigers got to Beckett for three runs in the third inning to take a 3-2 lead. Beckett allowed three hits to begin the frame and didn't get his first out until two runs were on the board. Prince Fielder capped the scoring with an RBI single.
"I made some pitches when I needed to and didn't make some other ones," Beckett said. "You're going to have five pitches in a game that you're going to have to make, and I think I made three of them today. And the other two cost me three runs in one inning."
The Tigers stretched the lead to 5-3 in the eighth, when Delmon Young hit a solo home run over the Green Monster off reliever Franklin Morales. They added two insurance runs in the ninth on RBIs from Fielder and Young.
Scherzer left after throwing 117 pitches over six-plus innings. He allowed three runs on seven hits and struck out six against two walks. The right-hander had allowed at least six runs in three of his previous four starts vs. Boston, but he won his fourth straight decision this month.
The Red Sox had a chance to tie the game at 4 in the seventh inning with Daniel Nava at the plate and Nick Punto on second. Nava scorched a ball to center, but it died just before it got to the wall and fell into the glove of Quintin Berry.
"It hung up there just enough, so I was able to get under it," Berry said.
Valentine was surprised the ball was caught.
"Early in the game the ball was traveling really well," said Valentine. "In batting practice it was traveling really well and it looked like it got dead there. I thought it was at least off the wall."
The loss snapped a three-game win streak for the Sox, but they are 14-6 in their last 20 games. Boston went 4-3 on its seven-game homestand and opens a three-game series in Toronto on Friday with Clay Buchholz on the mound.
"We lost tonight, but we're playing good baseball," said outfielder Scott Podsednik, who went 1-for-3 with an RBI. "I think there's something to be taken from this homestand. I think we've created some momentum. I think all the new faces are getting comfortable with one another, so hopefully we can build on the positives that happened here at home, get out on the road and play good baseball to win a series in Toronto."