William Nylander then made it a two-goal advantage at 18:25 on one of the numerous breakaways the Bruins allowed, especially as the game wore on.
As Bruins coach Bruce Cassidy put it, "We've been exposed by them on those breakaways, and you give up two, three in a row that period, so shame on us."
It wasn't their only issue.
"Obviously a lot of stuff we didn't do tonight," Bergeron said. "It was nothing we didn't expect, I guess. They're a team that works hard and gets their chances by putting the puck on net and converging. I think we didn't take care of the blue lines, that's where we got caught many times, and against a team like them, they're going to capitalize and get some momentum out of it."
Cassidy suggested some of the problems came from having relatively young defensemen, with Brandon Carlo and Connor Clifton each playing in his first Stanley Cup Playoff game. But Charlie McAvoy had played in 18, and Matt Grzelcyk had played in 11, and just as many issues were coming from Zdeno Chara -- veteran of 159 NHL playoff games heading into Thursday -- as the young players.
"Other guys tried to force it a little bit," Cassidy said. "Maybe turn down some opportunities to make an easier play, especially in the offensive end of it, offensive blue line, opportunity on the 2-on-1 we had with [Grzelcyk]. Next thing you know, it's in our net, so some of that hopefully they've learned that you have to make a quicker decision with it. … They've got a fast team, so that shouldn't be a surprise.
"Clearly on us to get that message across better Saturday."