BOSTON — The Boston Bruins are a case study in extremes on the blue line.

There are some prototypical bruisers: At 6-foot-9 and 250 pounds, 42-year-old Zdeno Chara anchors Boston’s first pairing and the 6-foot-5 Brandon Carlo is on the second line.

The rest of the defense? Take it down a notch: Torey Krug and Matt Grzelcyk are both just 5-9 and Connor Clifton is listed at 5-11.

Whatever they’re doing, it’s working: The Bruins defense and red-hot goaltender Tuukka Rask entered Game 1 of the Stanley Cup Final allowing a playoff-best 1.94 goals per game through the first three rounds. Boston allowed the Blues to score twice, but after Vladimir Tarasenko cashed in a turnover one minute into the second period, Boston closed the door over the final 29 minutes of the game on the way to a 4-2 victory.

Charlie McAvoy, Chara’s 6-foot linemate, said his team’s skating and puck movement makes up for what it may not have across the board in height.

“I think this kind of new-school NHL, you don’t need to be 6-5 anymore,” McAvoy said. “You can be Torey Krug and you can be a smaller, puck-moving guy who can outskate the forecheck and he uses his brain and Matt Grzelcyk — those guys skate. They’re incredible skaters, so it starts with that ability, and then their hockey IQ is through the roof.”

It all helps to put them in ideal situations in which they can work together to get out of bad spots, McAvoy said.

“They find the middle of the ice, they find the available guys, they play off instinct and are able to almost dictate the pace of play just through skating,” he said. “It doesn’t matter that they’re not 6-5. They’re able to close off plays in the corner based on skating and walling guys off.”

That doesn’t mean the smaller guys can’t deliver a blow when necessary.

Krug was the talk of Game 1 after he had his helmet knocked off, then got up, raced down the ice and toppled Robert Thomas with an open-ice body check .

Krug said the play hopefully was an example of the Bruins following through on one of the things they talk about prior every game.

“Just doing whatever the game needs,” Krug said. “We show up in critical moments. If the game needs a blocked shot, or a hit, or a good clean breakout pass — or you just need to ice the puck — we do whatever it takes. We just try to bring it.”

Coach Bruce Cassidy said he encourages that kind of intensity.

“The hit presented itself, he took it, but clean,” Cassidy said of Krug. “From my angle, no helmet and the way it went — yeah, it was old school. I thought it was a good energy boost for our team.”

While youth shined in Game 1, the glue of Boston’s defense is clearly Chara, a seven-time All-Star and member of Boston’s 2011 Cup team. He’s been nothing short of ageless this postseason, appearing in 17 of the Bruins’ 18 games during this run. He’s also willingly embraced a mentor role for his younger teammates.

He said Tuesday he has drawn inspiration from another Boston athlete with plenty of mileage — and plenty of success: New England Patriots quarterback Tom Brady, who is 41.

Brady did a voice over for a Bruins hype video that Chara posted on Instagram that ends with Chara repeating its tagline: “We are made for this.”

“It’s no secret that he’s one of those world athletes that everybody looks up to,” Chara said of Brady. “He’s been very successful at what he does and how he prepares himself. … I only have great experiences talking to him.”

Like Brady, Chara said that there was a recognition that he needed to adjust his game to compete at his age.

“You gotta be a little bit ahead of the game as far as seeing what’s happening with the players coming in and how skilled they are,” Chara said. “If you’re not then you’re gonna be way behind. …  The game got a lot faster than in the late 90s. … But I think if you work hard on your game and work hard to be better you can play a long time and in any type of game.”