BOSTON – David Desharnais and the Montreal Canadiens saw an opening when Zdeno Chara went to the penalty box, and they certainly made the most of it.

Max Pacioretty scored the tying goal in the third period and Desharnais put Montreal ahead to stay, leading the Canadiens to a 4-3 comeback win over the Boston Bruins on Sunday in a matchup of the Eastern Conference’s top teams.

Both goals came with Chara sitting in the penalty box.

“It’s big,” said Desharnais, who also scored in the first period. “He’s a key player for them. For him to not be on the ice is good for us, and we took advantage of it.”

Tomas Plekanec had the other goal for the Canadiens, who jumped two points ahead of Boston for first overall in the conference.

Bad feelings surfaced late in the second period. Alexei Emelin appeared to cross-check young Bruins star Tyler Seguin on the right hip, sending him to the ice in pain.

Chara raced in and nailed Emelin, and the pair squared off to the left of Montreal’s net, with the Boston captain throwing most of the punches. Seguin headed toward the dressing room but came back to the bench a few minutes later. Chara received an instigating penalty, fighting major and 10-minute misconduct, leaving Boston short-handed on defense for a good portion of the third.

“The guy just broke his stick cross-checking Tyler,” Chara said. “I was just reacting to it. He’s one of our best players and I’m not going to just watch him getting crushed like that.”

Chara’s teammates felt his actions were justified.

“Z knows the right time to step up and fight for his teammates — and tonight was the right time,” Bruins winger Brad Marchand said. “One of our guys that plays a lot of minutes takes a good shot.”

Bruins Coach Claude Julien was even more upset.

“The frustrating part is you end up with 17 minutes in the penalty box when you should have been on the power play,” he said before challenging the Canadiens, stating they faked some hits for penalties.

“There was a lot of embellishment,” he said. “That was embarrassing tonight. They have over 100 power plays and we all know why watching tonight. The embellishing is embarrassing for our game.”

Seguin, Patrice Bergeron and Dougie Hamilton scored for Boston, which had won six in a row. Tuukka Rask stopped 22 shots.