Sam Navarro-USA TODAY Sports

Toronto Maple Leafs head coach Sheldon Keefe was furious with his team’s lack of discipline during a 5-1 loss to the Boston Bruins in Game 1 of their first-round series.

Boston routed Toronto 5-1 during the opening game, punctuated by two power play goals from Jake DeBrusk despite being outshot 36-24. Keefe was particularly frustrated with Toronto’s first line of Tyler Bertuzzi, Auston Matthews and Max Domi, all of whom were penalized during Saturday’s contest.

“Careless penalties, Domi’s penalty obviously is the one that I would call an undisciplined penalty,” Keefe said post-game via Sports Illustrated’s David Alter. “I understand what he’s trying to do, but he crossed the line there, and can’t do that. But then, just the high sticks, and that kind of stuff, that’s just careless stuff. I don’t know if that’s something to do with the emotion or anything like that.”

Toronto failed to convert on any of its three power play opportunities, where William Nylander’s injury-related absence was profoundly felt.

“We’ve played without guys at different times and we’ve handled it very well,” Keefe said of Nylander’s absence. “We didn’t handle it very well tonight. We certainly missed him.

“But he has nothing to do with us taking too many penalties or giving up a 2-on-1.”

Domi was engaged with Bruins captain Brad Marchand from the outset of the contest, with the players exchanging pleasantries during the opening faceoff. During the second period, with the Bruins commanding a 3-0 lead, Domi slashed Marchand during the faceoff and the Bruins’ captain shook his wrist in pain. DeBrusk then scored his second power play goal of the game on the ensuing man advantage.

Boston converted 22.2 percent of its power play opportunities during the regular season, the seventh-best total in the league. If the Maple Leafs are to tie the series up, it has to remain disciplined at TD Garden in Game 2.

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