Matt Niskanen scored the game-winning goal for the Capitals, his second this week. (Michael Dwyer/AP)

Matt Niskanen has found himself at the center of three game-winning goal celebrations this past week, but none were bigger than the one at TD Garden on Saturday, when the whole team got to surround him.

His blast in overtime lifted the Washington Capitals to a 2-1 win over the Boston Bruins and to the 100-point mark for the season. The celebration was at once for the goal, for a hard-fought and emotional win and for reaching a three-digit point total with 17 games to go in the regular season.

This Niskanen clincher, scored 2 minutes 36 seconds into the extra period, came after he had the decisive assist Tuesday against Pittsburgh and goal Wednesday against Toronto. So how did the defenseman the Capitals have often referred to as “under the radar” manage to command the biggest spotlight this week?

“He changed his curve,” said Karl Alzner, Niskanen’s defensive partner. “That might have something to do with it. He’s putting pucks at the net. I guess he’s feeling pretty good with the puck right now.”

With Washington’s place atop the Eastern Conference essentially secure, the Capitals have admitted to having trouble staving off complacency 65 games into the season. The low point came Wednesday, when Washington played with what it considered an unacceptable amount of effort even though it earned a 3-2 win against the Maple Leafs, and the Capitals criticized themselves for it.

On Saturday, no matter what the result of the game, the Capitals had all of the ingredients they had been missing at times recently: good goaltending, good special teams and a fiery effort.

“There was a lot of battle on our bench,” Coach Barry Trotz said. “You see the guys getting stitched up and all of those things, so you’ve got to like that. I think it was a real good hockey game for us, for both sides.”

The game seemed to turn on an Alex Ovechkin penalty 5:36 into the second period with the Capitals trailing 1-0. Ovechkin was assessed a five-minute major penalty for boarding Boston’s Kevan Miller, and Miller would not return. A scrum broke out after the hit and Brad Marchand also went to the box for roughing, but the Capitals still would have to survive three shorthanded minutes.

“It’s hard,” said Ovechkin, who is listed at 239 pounds, 29 pounds heavier than Miller. “Obviously you don’t want to be in this position to take a penalty, but even the referee said I get five minutes because I was heavier than him, so it’s kind of strange. It is what it is.”

The penalty kill got tougher after Tom Wilson was called for interference, putting Washington down two players for 1:49. Boston has the seventh-ranked power play in the league, but Grubauer made eight saves during the two-man advantage, including one of the most impressive save sequences by a Capitals goalie this season. The Capitals got through the shorthanded time unscathed.

“That was a big kill,” center Jay Beagle said. “Gruby stood on his head. The momentum after the kill was, all right, let’s go after them and play five-on-five and win this hockey game.”

Through two periods, Grubauer had stopped 26 shots, one of his best performances of the year. Thanks to a strong third period by the team in front of him, Grubauer only saw four shots in the final 20 minutes. He has been a reliable backup for Washington, typically getting the second game of back-to-backs in place of Braden Holtby, when the rest of the team is not so fresh.

A defensive-zone turnover by Nicklas Backstrom resulted in a first-period goal by Patrice Bergeron 7:11 into the game. The deficit was nearly worse. Grubauer saved a shot by David Pastrnak, but Torey Krug punched in the rebound. Trotz challenged that the play was offsides, and the review came back in his favor, keeping the deficit to one goal.

“If it goes in, it’s a different game,” Grubauer said. “On the coach’s challenge, I think it killed their momentum a little bit.”

After the Capitals survived the flurry of shots during Boston’s five-on-three, they drew momentum from the penalty kill. In the Bruins’ zone, Alzner corralled a loose puck to keep the play alive, skating it behind the net and to the wall before relaying it to Ovechkin. Ovechkin got the puck to Backstrom, who flicked it through defenseman Zdeno Chara’s legs and to the crease for an easy Alzner tip-in goal with 6:52 left in the second period.

The tying goal set up the opportunity for Niskanen to net his latest winner. For a change, the Capitals got a win they were proud of, too.

“Heck of a hockey game,” Niskanen said. “Fun to be on top.”