Then the Red Sox rallied from a four-run deficit to set up Detroit for perhaps its most disheartening loss in a season already full of them.
Just when it seemed safe to count the Tigers out, they won for the first time in 20 chances when trailing after eight innings.
"It tells you a lot about our team," Polanco said. "We had some really tough at-bats against Papelbon to make something happen."
Boston had everything set up for its sixth consecutive win, rallying from an 8-4 deficit with its star closer on the mound. But Papelbon (2-1) blew his first save in 11 chances by allowing two unearned runs.
"We didn't get many breaks," Papelbon said. "When they get little breaks like that, they're going to make you pay for it."
Detroit had a season-high 18 hits, the most Boston has allowed this year.
"I thought I had a chance to go to second," Lugo said. "I bobbled the ball."
After Curtis Granderson's RBI groundout, Polanco blooped one over a leaping Lugo for his season-high fifth hit and Renteria trotted home with the winning run.
"I was just trying to put it in play and I was glad it just went over Lugo's head," Polanco said.
Todd Jones (1-0) pitched the ninth for Detroit, which snapped a five-game losing streak.
"I don't believe in momentum, but if we go on and do good, we might look back and say that was a big win," Tigers manager Jim Leyland said.
Kevin Youkilis hit two home runs, Mike Lowell hit a three-run homer in the seventh and pinch-hitter Dustin Pedroia had a tiebreaking single in the eighth for the Red Sox in a rally that went all for naught.
The Red Sox trailed 8-4 after five innings.
"We had a great comeback and we couldn't finish it," Boston manager Terry Francona said.
Youkilis has seven homers at Comerica Park, five more than he has at any venue as a visitor. The only other time he hit two home runs in a game was -- naturally -- in Detroit on Aug. 8, 2004.
Detroit went ahead 4-0 in the third -- scoring more than it did in the previous two losses to Boston -- and added four more runs over the next two innings.
It wasn't enough to hold off the Red Sox.
Detroit starter Armando Galarraga gave up five runs, seven hits in 5 1/3 innings. The rookie, who went into the rotation when Dontrelle Willis went on the disabled list, matched a career high with six strikeouts and walked only one in his fifth start.
Buchholz yielded a season-high 10 hits, five runs and struck out six over four innings, getting one more out than his season low.
- Red Sox RHP Curt Schilling is expected to play catch on flat ground Thursday, testing his ailing shoulder as he did Tuesday.
- Willis, who had a rehab start last week, is expected to pitch in the bullpen this weekend.
- Boston IF Alex Cora (right elbow sprain) began a rehab assignment Wednesday and was 2-for-4 with a run in seven innings at Triple A-Pawtucket.
- Red Sox RHP Daisuke Matsuzaka, who pitched with a cold Monday night, was feeling better Wednesday and is expected to have a higher pitch count Saturday at Minnesota.
- The game started only a minute late -- quite a feat with the heavy rain that soaked the field and created ponds on the tarp. But the game took 3 hours and 55 minutes to finish.
- Sheffield's RBI single in the third was the 1,582nd of his career, pulling him within one of former Tiger and Hall of Famer Al Kaline for 35th on the all-time list.
- Boston CF Jacoby Ellsbury had two stolen bases and is 22-for-22 in his career, the best start by a Red Sox rookie since 1920. The Red Sox have been successful in their past 20 steal attempts.