Watch: Blue Jays walk off Red Sox in extras to complete epic comeback

Guerrero Jr. began the 10th as the automatic runner on second base. Outfielder Daulton Varsho and right fielder George Springer were each walked by Red Sox relief pitcher Justin Slaten before Kirk delivered the game-winner.

The rally from the 6-0 deficit began with back-to-back homers from Kirk and Varsho off Red Sox starter Lucas Giolito, who has dealt with multiple injuries and was making his first start since signing a two-year, $38.5 million contract 16 months ago.

The epic walk-off single served as a fitting end to the catcher Kirk's bobble-arm night at the stadium and capped a two-RBI game for the sixth-year player. 

After splitting the first two games of the series with Boston, Toronto (14-16) will go for the series win on Thursday night and try to keep the momentum rolling from the thrilling comeback win on Wednesday.