Gagné seemed to improve down the stretch and was eventually added to the playoff roster. In the playoffs, he was most often used in games in which the Red Sox were winning by a wide margin, including his only World Series appearance in which he pitched a perfect ninth inning in a 13–1 Game 1 victory. The only exception to this was his appearance in Game 2 of the American League Championship Series against the Cleveland Indians. Brought into a tie game in the top of the 11th inning, Gagné took the loss after allowing the first two runs of a 7-run 11th inning.