This is Boston’s fifth loss in seven games.
Starter Josh Beckett was replaced by Alredo Aceves in the fourth inning after spraining his right ankle. Manager Terry Francona and trainer Mike Reinold came to the mound, and Beckett walked back to the dugout unassisted.
Blue Jays right-hander Henderson Alvarez pitched six scoreless innings, walked one and stuck out four.
The Red Sox threatened with runners on first and second in the fourth, but Josh Reddick struck out looking to end the inning.
Boston again had runners on first and second in the eighth after a two-out double by Adrian Gonzalez and an intentional pass to David Ortiz. The Sox hoped Kevin Youkilis could provide the breakthrough hit, but the third baseman went down swinging to kill the rally.
Jonathon Papelbon escaped trouble in the bottom of the 10th, striking out Adam Lind on three pitches with the bases loaded and two outs. Dan Wheeler (2-2) surrendered the walk-off blast the following inning, dropping the Red Sox another game behind the division leading Yankees.
Jon Lester will go for his 15th win on Tuesday against the Blue Jays at Rogers Centre, a 7:07 p.m. ET start.