While it’s true South and Blandina made some ticky-tack calls, it was ultimately the Bruins to blame for their parade to the penalty box.

Marco Sturm’s club was called for seven minors — including one double minor. The three third-period minors ultimately did them in.

“Good question,” said Sturm, when asked how his team can become more disciplined with regards to penalties. “You can show them, we can talk about it. I think we addressed it many, many times before. At some point, I think, it’s up to the players, too, a little bit. You have to be careful. You’ve got to know when to use your stick and maybe not. There’s a lot more to it.

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“So yeah, I think that slowly comes down to that. So, I think everyone has to ask himself, ‘Do I really have to take that penalty?’ Those are big deals because they could cost us games, points. Those kinds of points we will need at the end of the year. So, it definitely has to get better.”

The Bruins (20-17-1) led, 2-1, after the first period but never dented Canadiens goalie Jacob Fowler (26 saves), the former Boston College standout, again.

After Ivan Demidov tied it, 2-2, the Bruins appeared to take a 3-2 lead with just seconds left in the second, but Elias Lindholm’s would-be goal was disallowed for goalie interference.

The Bruins didn’t challenge despite replays appearing to show Juraj Slafkovsky and not David Pastrnak bumped Fowler.

“It’s always a group decision,” said Sturm, about whether to challenge. “I think we thought David had the stick in the goalie’s pads and he couldn’t move. And it was a non-goal call from the referee, too. So, you always have to think about that one, too. They don’t like to overrule things.”

Zachary Bolduc gave the Canadiens a 3-2 lead and this time the Bruins opted to challenge, feeling Nick Suzuki had interfered with Jeremy Swayman (23 saves).

The call was upheld; the Bruins were penalized for it and soon found themselves down two men when Tanner Jeannot was called for cross-checking.

Cole Caufield capitalized and moments later the Canadiens were back on a 5-on-3 when Hampus Lindholm was called for tripping. Suzuki made the Bruins pay again and a tight game quickly turned into a blowout.

Slafkovsky buried the final goal for the Canadiens (20-12-5).

The Bruins ended their five-game homestand at 1-3-1.

“It’s terrible. It stinks. Really, this whole homestand going into the break, it’s unfortunate,” said Alex Steeves, who had given Boston a 2-1 lead with a power-play goal in the first. “But I think it’s moments like these where you find out how tight the group is. And I know we have a tight group, and I know we’ll bounce back from this, and we’ll be stronger because of it.

“Stings for now, but we have three days to refresh mentally and come back ready for a huge push up until the Olympic break.”

It took Jeannot and Josh Anderson exactly three seconds to remind everyone on the Eastern Seaboard that this ancient rivalry has a strong heartbeat.

The two heavyweight wingers dropped the gloves and went at it in a start reminiscent of the first meeting between the old rivals in November.

Jeannot got the better of a willing Anderson, landing several big rights before landing on top of the Canadiens winger.

It brought the building to its feet and served notice that emotions and tempers would run hot in this one.

Nikita Zadorov and Arber Xhekaj then threw down the mitts for a center ice throw down, with both battlers landing blows before Zadorov scored the takedown.

“These guys have been awesome the whole season long. They are showing, they’re playing well. They got bigger roles,” said Pastrnak. “They’re in every night, so it’s easy to get into the game and you have guys like this and they’re amazing guys and teammates, so we’re lucky to have them.”

The Canadiens struck first when Sammy Blais, recently claimed off waivers from the Maple Leafs, scored his first goal for the Bleu, Blanc et Rouge.

Bruins center Marat Khusnutdinov tied it, 1-1, with his fifth goal of the season.Danielle Parhizkaran/Globe Staff

Marat Khusnutdinov tied it when the speedy winger slammed home a nifty cross slot pass from Mason Lohrei, who had frozen Oliver Kapanen at the blue line, by Fowler for his fifth goal of the season.

The Bruins took their first and only lead when Steeves rifled one from the dot with Demidov in the box for hooking. Steeves’s eighth goal of the season marked the fifth straight game the Bruins have connected on the power play.

A Bruins miscommunication in the neutral zone led to the Canadiens’ tying goal.

Pavel Zacha dropped a pass back to Zadorov and the big defenseman tried to bump it to Pastrnak, but it didn’t have juice and Demidov pounced. The slick winger broke in alone and went backhand-forehand to beat Swayman to make it 2-2 and set the stage for the calamitous third.

“It’s a tight game going to the third and again, a couple mistakes, whether it’s mental or penalties,” said Pastrnak. “I mean, at the end of the day, you give up two 5-on-3s … I think if we get two 5-on-3s in the third period, I think we will win the game.”

Jim McBride can be reached at james.mcbride@globe.com. Follow him @globejimmcbride.