With the game tied 4-4 in the eighth inning, Boston outfielder Daniel Nava dropped a fly ball before reliever Andrew Miller made an errant throw that led to Detroit's go-ahead rally.
Prince Fielder delivered a two-run single and the Tigers scored three runs in the critical eighth to key their victory and give them a four-game lead atop the American League Central.
Despite the defeat, the Red Sox (45-33) remained two games in front of Baltimore (42-34) in the AL East.
The Orioles had a chance to gain some ground, but they ran into the red-hot Toronto Blue Jays, who routed them 13-5 for a team record-equalling 11th straight win.
Toronto buried Baltimore early by building a 9-0 lead through three innings and cruised in the finale of a three-game home sweep.
Edwin Encarnacion hit his 21st home run and finished with three hits and four RBIs, while Jose Bautista added three RBIs to help the Blue Jays match their record winning streak, last accomplished in 1998.
In Washington, Michael Cuddyer continued his own hot stretch by extending his Major League-best hitting streak to 21 games in Colorado's 7-6 win over Washington.
Cuddyer homered in his first at-bat in the second inning and ended up 3-for-4 with three RBIs.
He surpassed St. Louis infielder David Freese, who had a 20-game hit streak that ended earlier this month, for the longest hitting stretch this season.
The Rockies grabbed a 7-0 lead but had to hold on as the Nationals tallied four runs in the eighth to pull within one.
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