BOSTON — They’re planning, plotting and strategizing, trying to nail down perfect-world scenarios that will cover at least the start of the series. Sometimes the Bruins will get their preferred head-to-head personnel matchups; often they won’t.

Long confident that any of their four forward lines can handle shifts against an opponent’s No. 1 or No. 2 group, the B’s don’t stress if their preferred plan doesn’t pan out. But as they prepare for Game 1 of the Stanley Cup Final on Monday night, the Bruins also find themselves relatively assured that they won’t have to obsess over which defense pairs compete against whoever the Blues have on the ice at a given moment.

The B’s will still try to give captain Zdeno Chara and partner Charlie McAvoy the majority of the shifts against the Blues’ most dangerous lines, and attempt to make sure that Matt Grzelcyk and rookie Connor Clifton get most of their ice time against Bottom 6 forwards. They’re also secure that the No. 2 pairing of Torey Krug and Brandon Carlo can handle anything thrown at them, from the top of the Blues’ depth chart to the bottom.

“They’ve been dynamite for us,” Bruins coach Bruce Cassidy said. “It’s allowed us to really balance our pairs, and match up a lot better.”

The Krug-Carlo pairing was formed late last season, but Carlo’s season-ending ankle fracture delayed its postseason debut until this spring. Carlo’s defense-first mentality hasn’t changed (he’s the only one of 19 skaters to play 14 games or more without scoring a goal), but Krug has suppressed his offensive instincts more than at any time in his six-year NHL career. He’s still the Bruins’ most productive blue-liner through 17 games with 12 points (one goal, 11 assists), but only five of the points (all assists) have been scored at even strength, and his plus-6 rating — same as Carlo — is the best mark of his playoff career. He was minus-5 in 11 postseason games a year ago.

“You’re always going to get the power play acumen from (Krug),” Cassidy said, “and he’s going to make his breakout passes. But he’s taking a lot of pride in playing on the other side of the puck.

“He’s boxing out big guys every night — he’s committed to that. He’s not leaving the (defensive) zone early; he’s making sure the puck’s going out of the zone before he is. The commitment to stay in the battle has been excellent.”

That, Cassidy said, adds up to “all the little things that make you a good defensive defenseman” — which has never been Krug’s reputation, despite his career-long battle to improve that aspect of his game, and perhaps get some credit for it.

It’s coming now.

“Torey’s been playing great, and he’s helping me along the way, as well,” Carlo said. “He’s been doing a really good job on the defensive side of things.”

Carlo and Krug have made adjustments during the playoffs.

“There’s been times throughout the regular season where we kind of have a little bit of an agreement — I’ll try to box out the guy in front, and Torey scopes out from there,” Carlo said. “But in the playoffs, there’s been times when he’s boxing out, and he’s doing a fantastic job of keeping guys to the outside, playing hard in that ice there.

“He’s been doing really well on the defensive side, and it’s boosting my side of the game, as well.”

The Krug-Carlo pairing has been so steady and valuable that Cassidy has taken pains not to break it up. The Bruins’ defense corps hasn’t had veteran Kevan Miller (knee) for the entire postseason, and lost Chara (injury) and McAvoy (NHL suspension) for one game apiece, but the coach has found other ways to plug gaps without separating Krug — at 5-foot-9, 186 pounds all but tied with Grzelcyk (5-9, 174) for the distinction of being the Bruins’ smallest defenseman — and the 6-5, 212-pound Carlo.

Krug is proud of that.

“We still try to get matched against certain lines,” he said, “but we’ve also been told from Day 1 that we can play against anyone, and not to worry too much about matchups: Just play the guys who are across from you.

“We know other pairs, other people, may get the headlines, but we’re just going to do our thing quietly. We’ve done that for a long time; it’s just that now it’s on a different stage.”

Big turnout for scrimmage: The Bruins held their much anticipated scrimmage on Thursday night at TD Garden, where a big crowd watched the B’s and Black Aces taxi squad divide a practice into two 25-minute halves. Players wore their usual practice jerseys instead of official game jerseys with names and numbers.

No. 1 goalie Tuukka Rask, who hasn’t played against anything like live competition since last Thursday’s sweep-clinching 4-0 shutout at Carolina, surrendered two goals in his half of the scrimmage.

Captain Zdeno Chara, who was a late scratch for Game 4 of the Eastern Conference finals last Thursday, participated in all aspects of the scrimmage. Center David Krejci was ill, and didn’t participate.

Players were given Friday off, and will practice on Saturday and Sunday. Game 1 is Monday night at TD Garden.