Into the last days of training camp, the Boston Bruins’ line charts to start the season were pretty much set.

Until Torey Krug (jaw) and Patrice Bergeron (lower body) went down with recent injuries – and David Backes with diverticulitis.

Seems like yesterday that Ryan Spooner was headed elsewhere with trade rumors a daily dynamic. Thursday night against Nashville, he’s bumped up from third-line center to first between Brad Marchand and rookie Anders Bjork.

Sean Kuraly, a Providence Bruin staple last season, made the most of his playoff presence in April’s six-game set against Ottawa. Thursday night, he’s in Spooner’s slot.

Frank Vatrano, still trying to find a groove in Year 3, on the right side of Kuraly.

P-Bruin Matt Grzeclyk was on the third D-pairing with Adam McQuaid, creating a duo of rookies and former BU Terriers in the lineup in Grzelcyk and McAvoy.

Such was the juggling act by Bruce Cassidy to begin the first of 82 with three prized pieces of the Black-and-Gold on the sidelines. Not exactly what GM Don Sweeney and Cassidy had in mind – or place – these past weeks of training camp.

And not even close to what transpired over the 60 minutes of play Thursday night, especially when Noel Acciari left the game early in the second period.

Before the opening faceoff, that entire starting lineup Thursday against the defending Western Conference champs:

Marchand-Spooner-Bjork
Jake DeBrusk-David Krejci-David Pastrnak
Matt Beleskey-Kuraly-Vatrano
Tim Schaller-Riley Nash-Acciari

On defense:

Zdeno Chara-Brandon Carlo
Kevan Miller-Charlie McAvoy
Matt Grzeclyk-Adam McQuaid

By the time the fans settled into their seats, that lineup was fodder for the TD Garden cleanup crew as Cassidy rolled out more forward combinations over three periods than sundae combos at a pre-school fundraiser.

The only piece intact? Tuukka Rask between the pipes.

The only other one even close was the Beleskey-Kuraly-Vatrano trio.

Even Nash jumped from the fourth line to three minutes on the first PP unit – taking Bergeron’s spot on the bumper – and 5:07 on the penalty kill; Gryzelcyk 2:56 on the PP.

“We were running a little bit short on the forwards, so Butch [Bruce Cassidy] did what he had to do,” Pastrnak said in understatement about the myriad of line combinations.

“The game dictates it,” Cassidy assessed postgame. “We lost a player early, a forward [Acciari], so right away you know you’re going to be juggling. I mean, I tend to tinker anyway. We’ve put some guys in the lineup with players they haven’t played with a lot in preseason. We had them together in camp, but still there’s no regular season chemistry between – then you lose Bergy [Patrice Bergeron], Backes [David Backes], so this was going to be a shuffling from start to finish and maybe we’ve found something with a few combinations tonight.”

Here is what we learned from the season-opening 4-3 win over the Predators.

B’s off and running on the PP

The Preds took the rare double-minor penalties for slashing and cross-checking at 7:58 of the first to put the B’s on a 5-on-3 power play. Spooner, Krejci and Marchand the first PP unit. But it was the defense that produced Boston’s first goal of the season at 8:37 when McAvoy shoveled a pass across to Pastrnak, who launched a 40-foot laser past Pekka Rinne for the 1-0 lead; Krejci also assisting.

Adam McQuaid would log the first fisticuffs of the season when he and Cody McLeod exchanged pleasantries at 10:56. McQuaid held his own against the reigning NHL leader with 19 fighting majors last season.

A Pastrnak gaffe off a Krejci faceoff with 10 ticks remaining put the puck on Viktor Arvidsson’s stick with Rask dead to rights from 10 feet out. Arvidsson promptly whistled it to twine for the tying goal.

DeBrusk and Bjork and McAvoy make good in debuts

The 2015 first-round pick – with his mom and dad, a former Edmonton Oiler, in the stands – finished off a pretty 3-on-2 led by Bjork who sent Krejci down the left dasher. His shovel pass put DeBrusk in alone on Rinne. He wasted no time deking it home for the one-goal lead at 5:48 of the second period.

Three minutes later, DeBrusk was in alone, but Rinne stole that show with a sparkling glove save.

At 15:43 McAvoy would retrieve the puck after scoring his first NHL goal on a veteran-like rush with Krejci to Rinne’s crease before his wrister gave Boston a 3-1 lead.

The trio ended with a total of two goals and three assists – and even more impressive, a combined plus-5. On occasion, DeBrusk and Bjork were on the same line with Krejci.

“It allows Krech [David Krejci] some youth and some speed on his wings,” Cassidy said about the unique line formation. “They both do a little bit of playmaking and scoring, so it could be a good line.

“They all had good moments,” Cassidy followed about the B’s youth, “they all had learning moments throughout the course of the game, as we expected, but they stayed with it, they’re good players and obviously helped us win a hockey game.”

Last two minutes of mayhem

The last two minutes had more combinations of penalties and goals than Cassidy’s line changes. Brad Marchand’s short-handed open-netter at 17:07 with Rinne pulled and Miller in the box for a Pred’s 6-on-4 pushed the lead to 4-1. But Chara took two and again with Rinne pulled, the Preds took a 6-on-3 to a second goal by Scott Hartnell at 18:12. A 6-on-4 produced a third goal by Filip Forsberg at 19:25 for the 4-3 final.

“I think we mismanaged a couple of pucks and took a penalty on plays that we could have got one out and then kept it in play,” Cassidy said about the frantic final moments in the third. “So right away you’re scrambling there. The goals, obviously they made plays, that’s them making plays. So, we put ourselves in that tough spot.”

About future juggling

“We’ll look at the video obviously, again,” Cassidy said about his lines, “talk to those key players, see how their chemistry went. Sometimes on the ice, it doesn’t look the same as when you talk to them, so we’ll see what we come up with on Monday.”

That would be when the Colorado Avalanche come to town. Get used to the tinkering and juggling – if you haven’t already.