The Maple Leafs started off strong with a goal from Morgan Rielly midway through the first period. But the Bruins quickly responded with power-play markers from Brad Marchand and Torey Krug to take a 2-1 lead into the first intermission.
"We were really ready, we were jumping big time," Maple Leafs head coach Mike Babcock said postgame according to TSN's Mark Masters. "But then, as soon as we had a little adversity and then they scored twice, we didn't recover. I don't know if that's the emotions got the better of us or we couldn't get 'er back in check"
Jake DeBrusk added the eventual game-winner in the second period when he connected with David Krejci for a pretty give-and-go tally. The Bruins took over in the middle frame, outshooting the Leafs 16-9 and controlling the play.
"They had one of the best periods they've had all playoffs in the second," Babcock said according to Masters. "We didn't execute or play fast enough or well enough."
Auston Matthews pulled the Leafs within one in the third period with his fifth goal of the series, but then Marchand put the game on ice with an empty-net goal.
"It's all small details," Matthews said, according to Masters. "Neither team is making many mistakes ... tonight our first five-to-six minutes (were) good and then their (power play) got them going and then we didn't really have an answer until the 3rd period ..."
Bruins netminder Tuukka Rask held down the fort with 22 saves for his 38th career postseason victory.
The series will go the distance for the third straight time between these two fierce rivals, as Boston hosted Game 7 in 2013 and 2018 as well.