James van Riemsdyk and Pastrnak scored for the Bruins, who are the No. 2 seed from the Atlantic Division. Jeremy Swayman made 24 saves in his second straight start.
“What went into the decision (to play Swayman again over Linus Ullmark) was we rotated the first two games and then Swayman played so well, we were going to go with the hot hand,” Boston coach Jim Montgomery said.
Mitch Marner scored for the Maple Leafs, who are the No. 3 seed from the Atlantic. Ilya Samsonov was pulled after allowing three goals on 17 shots through two periods, and Joseph Woll made five saves in relief.
“Obviously tough when this was an important game,” Toronto defenseman Morgan Rielly said. “I think we have to look to be better, we’ve got areas to clean up. I think more things going towards their net. I thought we turned down some shots. When we did get offensive-zone time and did get things towards their net, there was some stuff happening but not nearly enough. Neutral zone, they did a good job of clogging it up.”
Van Riemsdyk put the Bruins up 1-0 at 15:09 of the first period. Ryan Reaves’ clearing attempt along the right boards went off Boston defenseman Mason Lohrei’s stick and bounced to van Riemsdyk in the left circle before he made a backhand deke to beat Samsonov.
“It gives us another line that is going to score,” Montgomery said about the play of van Riemsdyk, who was a healthy scratch for the first two games of the series. “Besides how good he is on the power play, how effective he can be at 5-on-5 offensively.”
The Bruins went up 3-0 at 19:18. After Marchand chipped a loose puck past TJ Brodie in the high slot, he passed to Pastrnak, who one-timed a shot past a sprawling Samsonov on a 2-on-0.