The walk-off win was Boston's second in as many days, after David Ortiz hit a three-run double to win Saturday's game. It was the Red Sox's first walk-off victory on an error since Sept. 3, 2008, against the Orioles.
"You know what, we got a bunt down, and when you get something down good, things happen," manager Terry Francona said. "They're in a tough spot there. The icing on the cake was that they threw it away. We made them throw strikes and took the balls and took advantage of the mistake."
Yet, before the Sox walked off, the Tigers managed to score three runs in the top of the ninth after being blanked for eight innings by Red Sox starter Clay Buchholz.
Buchholz came out to pitch the ninth, but he was relieved by Papelbon after giving up a shallow single into right field to Will Rhymes and a walk to Ryan Raburn.
With runners on first and second and no out, Miguel Cabrera belted a double off the wall in center field to cut the lead to 3-2. Jhonny Peralta then singled to center to score pinch-runner Don Kelly and tie the game at 3.
"It's exactly what I wanted to do. I went fastball up and in. I looked at the replay and it kind of bailed out in there," Papelbon said. "[Cabrera] was probably looking in there more than I was expecting, but right now, he's a Triple Crown hitter and he's hitting pitchers' pitches, and there's not much you can do about it."
Besides giving up the hits to Cabrera and Peralta, Papelbon said blowing the save was difficult because of how well Buchholz pitched.
"It's obviously my job, and Clay's been one of our best pitchers this year," Papelbon said. "As a closer, you want to protect those wins for your starters and you take pride in it, and obviously I wasn't able to do that today.
"It stings a little bit because you know that's what they work for, the wins, and I work for the saves, and neither one of them happened today."
Picking up where he left off in Anaheim, Buchholz dazzled in his first home start since coming off the disabled list, pitching eight-plus innings, and giving up two runs on three hits.
Before allowing the two runs in the ninth, Buchholz had thrown 14 1/3 straight scoreless innings.
"The team won, that is the most important thing. It is tough to go out there and throw eight innings and have the lead. I just didn't get it done in the ninth inning," Buchholz said. "All I needed to do was throw a strike down in the zone and get a ground ball out of it and Miguel would have come up with no one on. That is a situation I wanted. Things didn't happen that way.
"Pap is one of the best in the game and I will give the ball to him any day. It didn't happen today, but we fortunately got the win."
Detroit's bats were silenced by Buchholz most of the day, with the Tigers getting only two runners in scoring position against the All-Star righty.
"We played eight innings and didn't do anything offensively," Tigers manager Jim Leyland said. "If we score two runs early, we win the game."
Thanks to the bottom of the Red Sox's order, the team got on the board first in the second, on an RBI single to left field by Patterson that scored Adrian Beltre from third.
In the third, Kevin Youkilis singled and Ortiz walked, and Beltre singled home Youkilis before Ryan Kalish hit a sacrifice fly to center field, scoring Ortiz.
Beltre recorded his team-high 39th multihit game, which leads all Major League third basemen.
The Sox made Tigers starter Justin Verlander work throughout. In the first three innings, Verlander threw 75 pitches, 31 of which came in the two-run third.
In the three-game series against the Tigers, the Sox scored eight runs in the ninth, including four Friday, three Saturday and one Sunday.
"This team has a lot of character. We have had a lot of ups and downs this year," Buchholz said. "A lot of things have happened that could have caused anyone on this team to give in. Everyone has done the little things right to win ballgames and keep ourselves in contention."