On a night in which they lost their best defenceman, the Maple Leafs rallied for one of their gutsiest victories of the regular season.

Capped by Mitch Marner’s second goal of the night in overtime against the Boston Bruins, the Leafs won 5-4, taking three of four from their Atlantic Division rivals in 2024-25.

The cost was defenceman Chris Tanev, who departed the game in the first period with an upper-body injury. And William Nylander didn’t play in overtime as he appeared to be favouring his left arm on the bench.

Our takeaways from the victory, which kept the Leafs in first place in the Atlantic:

NO REPLACING TANEV

Tanev will be evaluated again on Wednesday, and Luke Fox of Sportsnet reported after the game Tanev was seen leaving TD Garden with his right arm in a sling.

There’s no way to sugarcoat it: If Tanev is out of the lineup for an extended period, it’s a huge blow to the Leafs, one that would be difficult to overcome.

The 35-year-old has been the Leafs’ best defenceman in the first year of a six-year pact, providing an example every night of how the job should be done properly.

“One of the best D-men in the league, in my opinion,” Morgan Rielly told media in Boston after the game. “Important to the penalty kill, he plays big minutes. He plays hard minutes against the other team’s best players. He brings a lot to our team.”

The Leafs’ defence corps managed to get through on Tuesday without Tanev, but asking the group to do it game in, game out, would be a great responsibility.

We would hate to look too far ahead — and it’s looking ahead only to next week — but would general manager Brad Treliving have to change course and try to acquire a bigger defensive piece than a depth defenceman before the March 7 trade deadline?

Already, we’re thinking Treliving would be stretching the prospects cupboard thin if he had to trade Fraser Minten or Easton Cowan to land, say, Brayden Schenn of the St. Louis Blues or Scott Laughton of the Philadelphia Flyers, if not someone else. The Leafs don’t have a first-round pick this year. What would be left to try to fill a Tanev-sized hole? It’s a lot to potentially think about, and a lot more than Treliving needed to possibly have on his plate.

“You look at the way that he blocks shots, the way he is fearless in front of the net, his penalty-killing ability,” goalie Anthony Stolarz said. “Hopefully it’s nothing serious (and) he’s not out too long.”

As for Nylander, coach Craig Berube told media in Boston that something was bothering the star winger. As with Tanev, the Leafs will keep their fingers crossed.

MARNER MAGIC

Five nights after he set up Connor McDavid for an overtime winner to send Canada into a frenzy with a 4 Nations Face-Off title against the United States, Marner was at it again, supplying the difference in the extra period after the Leafs erased a 3-0 Bruins lead and then didn’t flinch when David Pastrnak put his team ahead in the third period.

A last-minute goal by Pontus Holmberg set the table for OT, when Leafs captain Auston Matthews sent Marner in alone on a breakaway, which didn’t end well for Bruins goalie Jeremy Swayman.

Marner played 25 minutes, 41 seconds, most among Leafs forwards.

“He had a good experience, and I thought he played great (at the 4 Nations),” Rielly said. “And to win the tournament is great.

“It would be easy for him to change, or get caught up in hanging out with all the big dogs, but he just comes back, and he’s right back to his old self. We love him.”

Said Marner afterward: “We didn’t quit and that’s something you like to see out of our team.”

Marner said what happened last Thursday in the same building was not on his mind.

“Not much, to be honest,” Marner said. “It was a really cool memory, really cool thing to have and enjoy, but now different team back with the Leafers and we want to win games and keep going.”

Morgan Rielly, centre, celebrates his goal on Tuesday for the Leafs.
Maple Leafs defenceman Morgan Rielly (centre) celebrates with teammates after scoring a goal against the Boston Bruins on Tuesday. Rielly also added three assists on the night. Charles Krupa/AP

TEAM EFFORT

Rielly had a goal and three assists, including his 500th NHL point.

Stolarz again was outstanding in the Leafs net, making 32 saves.

And there were Nick Robertson and Holmberg, each scoring again as the Leafs won for the third time in three games coming out of the break.

It’s a great look for both with the trade deadline bearing down. We’re still not sure how the Leafs forward dust will settle once the deadline passes, but both Robertson and Holmberg are making a case to be taken seriously once the playoffs start.

That they were on the ice in the final minute of regulation and provided the winning goal speaks to the Berube’s confidence in them.

“I’m grateful for an opportunity to get to go on the ice in crunch time,” Robertson said. “We have to perform. Fortunately, Holmer buried his shot there.

“I like the physicality of my game, because that helps everything else and keeps me in the game. The coaches, that’s what they want. We need to be physical. These games are not going to be easy, especially with playoffs coming up. We want to have that mentality right now.”

It’s working, no doubt.

X: @koshtorontosun