The Maple Leafs still trail the Bruins 3-2 in their Eastern Conference quarterfinal series. Toronto won in Boston for the second time in the series, but has yet to win at home -- something the Maple Leafs will have to do in Game 6 on Sunday to force a deciding game.
Reimer, experiencing the NHL playoffs for the first time, gave up 15 goals in the previous four games against the Bruins.
Having been challenged by Coach Randy Carlyle to perform better, Reimer allowed only a third-period goal to Zdeno Chara that brought the Bruins within one with 8:48 to play.
Boston could not beat Reimer again and came up short despite a solid effort in goal from Tuukka Rask.
Rask finished with 31 saves after turning in a 45-save effort in Boston's 4-3 overtime win in Toronto on Wednesday.