MONTREAL — Mattias Samuelsson stood at his locker in Montreal’s cramped visiting dressing room after a hard-fought 3-2 win over the Canadiens. He had a bruise near his eye, his lip swollen beneath his fully grown playoff beard. The Buffalo Sabres defenseman was the picture of playoff hockey after giving a performance that matched the look.

The Sabres came into this game trailing two games to one. They had just lost the last two games by a combined score of 11-3, including a 6-2 shellacking in Game 3 at the Bell Centre. When a performance like that happens in a market like this one, it feels like the whole hockey world is watching. The questions were loud about whether the Sabres had hit a wall or met a superior opponent.

Their defensive-zone structure was a mess early in this series. The Sabres couldn’t break the puck out of their own zone cleanly and were making constant mistakes in their own end. The front of their net was too inviting a place for Montreal Canadiens forwards. What Buffalo needed was to calm down and tighten up its defensive game.

Enter Samuelsson, Buffalo’s eraser on the blue line. Some of his teammates didn’t necessarily calm down in this game. Rasmus Dahlin, Tage Thompson, Bowen Byram and Jason Zucker piled up a combined 16 penalty minutes between them. While four of Buffalo’s leaders sat in the penalty box, Samuelsson was eating up short-handed ice time. He finished the game with more than seven minutes of short-handed ice time, blocked a team-leading six shots and led the team with six hits. He also scored the game’s first goal with a perfect shot to beat Jakub Dobeš on the rush.

“He was a beast,” Sabres coach Lindy Ruff said. “He was a beast down low. I think his effort that just spills off into other players, from his physicality, to end up being involved in the offense all the time. But his PK work, his stick, I thought was great. He had a real good night for him.”

Samuelsson has been a revelation for Sabres general manager Jarmo Kekäläinen. Before he got to Buffalo, he didn’t realize just how good Samuelsson is and how important he could be to the team’s success. He is the type of player whose value is more obvious to those who see him every day. And in fairness, few outside of Buffalo got to see much of Samuelsson the last few years. He played through injury and was limited to 62 games last season and 41 the year before.

This season, Samuelsson played 78 games, set a career high with 13 goals and played 22:50 per game. He had the biggest single-season turnaround of any Sabres player.

Samuelsson was wearing the “A” on his jersey in Game 4, and it was fitting. He was the leader the Sabres needed to survive a game in which Montreal’s electric power play got seven tries. Ruff didn’t agree with all of the penalty calls but said it’s the time of year when there are some light penalties being called and a bit of embellishment might be happening.

“It’s the time of year where a player is going to do his best to make whatever call it is seem like it’s almost the end of the world,” Ruff said.

The Sabres didn’t handle that well. Byram took two high-sticking penalties totaling six minutes. Thompson got called for a light cross-checking penalty when Kaiden Guhle sold a shove. Guhle also sold an early Dahlin interference penalty. Dahlin earned another interference penalty later, and Zucker’s roughing penalty was careless.

“Our kill has been unbelievable all year long,” Thompson said. “This is probably one of the best power plays we’ve seen, but they’ve done an unbelievable job. Guys like Sammy are a big piece of that, putting their body on the line, blocking shots, selling out. Those are things that don’t look pretty on TV or to fans watching, but that’s stuff on the bench that gets us just as jacked as scoring a goal.”

Montreal’s power play could have been a difference-maker in this game. After a hot start, the Sabres had a 1-0 lead and an 8-1 advantage in shots eight minutes into the first period. But when Jack Quinn’s goal was overturned after an odd double review situation because officials ruled Konsta Helenius had interfered with Dobeš, the Canadiens were able to collect themselves. They got a goal from Alex Newhook a few minutes later and a power-play goal from Cole Caufield late in the period to get a 2-1 lead.

In the second period, the Sabres had three penalties. They weathered that storm in part because of Samuelsson’s work on the penalty kill. He and Conor Timmins both finished with more than seven minutes of short-handed ice time. Three forwards had more than five minutes of ice time on the penalty kill. And goalie Ukko-Pekka Luukkonen stopped nine of the 10 shots he faced on the penalty kill, including three high-danger saves. The Canadiens finished the night 1-7 with the man advantage.

“I mean, not the most fun,” Samuelsson said of all the short-handed ice time. “They have a good power play. Yeah, it’s tough. I’m just out there trying to make reads, break it up, help the team wherever I can. Tonight was definitely more penalty killing than anything else. Seven minutes on the kill definitely isn’t fun.”

The playoffs are about finding a way to win by any means necessary. It doesn’t matter how it happens. This game had a lot of weird moments. There was an overturned goal, and Thompson scored a goal when he dumped the puck hard into the corner and it bounced out toward the net, off Dobeš, and in.

“That felt like the hockey gods just giving us one back,” Samuelsson said. “We’ll take it any way we can. I was fired up.”

The Sabres needed to kill off another penalty to start the third period. A few minutes after they did so, Zach Benson got the winning goal on the power play.

That’s when Buffalo was able to lock the game down late, as it has done so often this season. Ruff said he felt like the Sabres finally looked like themselves Tuesday night after two straight sloppy games, and that was especially the case in the third period.

“We played more direct, simpler, put pucks behind them,” Samuelsson said. “We had poor puck management in 2 and 3. Just gave them free stuff. In the playoffs, it’s pretty hard to win games like that. Just more responsible tonight, better with the puck, better details in the D-zone.”

Despite all the talk about the offensive firepower in this series and how much open ice has been available, the Sabres can win with defense. They’ve shown that all season. And Samuelsson is a big reason. Now they’re heading back to Buffalo with the series tied 2-2.

“I thought tonight we finally tightened things up,” Ruff said. “We finally got to the place where we need to be. It looked like our team again, from the start of the game to the way we finished the game.”