First-year coach Jim Montgomery led the Bruins to a record-setting regular season, but a loss Sunday in Game 7 against the Panthers would end their season in the first round of the playoffs. Wilfredo Lee/Associated Press

SUNRISE, Fla. — The Bruins are staring down two vastly different scenarios on Sunday night when they face the Florida Panthers in a Game 7 at TD Garden that already has Bruins fans white-knuckling their arm chairs.

Behind Door No. 1? It’s the opportunity to prove they are the better team, which they are. They have a chance to learn from their mistakes, from the coaching staff on down (there have been a few whoppers), and come out on the other side stronger and smarter for having gone through the fire.

What is behind Door No. 2 is decidedly less palatable. From a local perspective, a loss in Game 7 would join this team at the hip with the 1971 Bruins as a colossal playoff flop. Of a more recent vintage, it would link them to the 2019 Tampa Bay Lightning. Both teams had record-setting regular seasons only to be bounced in the first round.

But there is a big difference between these Bruins and both the ’71 Black and Gold and ’19 Bolts. The latter two teams were still ascendant franchises who could and did make good on their do-over opportunities.

For the 2022-23 Bruins, this is it. Age and a coming salary cap crunch dictate that this team will at least be partially detonated.

Yeah, there’s quite a bit of pressure involved on Sunday evening, even more than your average Game 7. And it’s all on the Bruins.

So how did we get here?

The Bruins were in full control of this series, up 3-1 with a chance to close out the series on home ice in Game 5. Then they decided to get cute. With the return of Patrice Bergeron from an injury he suffered in Game 82, Coach Jim Montgomery went with unfamiliar line combinations. He split up Bergeron and Brad Marchand – a pairing that’s been working for a dozen years – to try Bergeron with David Pastrnak and Tyler Bertuzzi, a trio that had never skated together as a unit.

It looked like it. They got hemmed in their own end and gave up the first goal of the game when Bertuzzi threw the puck into his own slot. They would play catch-up all night and, it should be noted that as crazy as this series has been, the team that scores the first goal has won all six games.

There was also the questionable choice to play rookie Jakub Lauko over Trent Frederic, who had undergone his own playoff baptismal fire last season but didn’t get a chance to show he’d learned anything from it. Lauko committed two penalties, the second one a third-period call that led to another Florida go-ahead goal.

And there were signs that Linus Ullmark was tiring in that Game 5. All three regulation goals were Grade A opportunities, but when he’s been on his game, he would have stopped at least one of them. It very well could have been physical fatigue that led to his mental mistake on the giveaway that led to overtime game-winner.

Game 6 presented a great chance to lean on the depth about which the club has rightly boasted all year. From our standpoint, it appeared to be the perfect time to start Jeremy Swayman, who would have been perfectly capable of giving a winning performance, especially handed five goals with which to work. Even if they’d lost, they could have come back with a rested Ullmark for Game 7. But the collaborative decision was made to stick with Ullmark, and he gave up six. Now the choice for Game 7 is either an apparently weary-looking Ullmark or Swayman, who hasn’t played since April 13.

One more Game 6 personnel choice that backfired was inserting Connor Clifton for Matt Grzelcyk. Clifton is unquestionably a gamer, but from the get-go it appeared he was trying too hard to make an impact. In the first period, he was whistled for charging and had a costly turnover that led to the Panthers’ second goal. In the third period, his clear attempt was stopped at the blue line and resulted in the winning goal. He was minus-3 and the Clifton-Derek Forbort pairing has not clicked like it did in last year’s post-season.

Yes, mistakes have been made. There have also been some straight-up subpar performances, such as Hampus Lindholm’s 0-0-0 effort so far.

But the Bruins still have a chance to flush all that. And if you’re looking for a positive development from Game 6, it is that the dynamic version of David Pastrnak (two goals, seven shots) returned. Perhaps that was tied to big brother David Krejci being back in the lineup, perhaps not. But Pastrnak has the ability to tip the scales in the Bruins’ favor by himself.

A win in Game 7 could be cathartic and could set the Bruins up for a long run, just like first-round Game 7 wins did in 2011, 2013 and 2019.

A loss would be calamitous. If this is indeed the last seasons for estimable Bergeron and Krejci, they do not deserve to go out that way.