After a promising start to Game 4, the Bruins’ season is hanging by the thread.

And they’ve got more than one beef with the National Hockey League because of it.

The B’s squandered a 2-0 lead and lost 3-2 to the Florida Panthers at the Garden to fall into a 3-1 series hole. The game was tied in the third period by the new Public Enemy No. 1 in Sam Bennett on a highly disputed goal.

Sasha Barkov then scored the eventual game-winner at 7:31.

With their captain Brad Marchand unable to go with a suspected concussion, thanks to a Bennett cheap shot that went unpunished by the Game 3 on-ice officials as well as the Department of Player Safety, the Bruins came out of the chute looking to make some sort of statement.

It didn’t take long. On the first shift of the game, Charlie McAvoy lined up Sam Reinhart inside the Florida blue line and absolutely blew him up with a thunderous hit.

With the Garden buzzing, the B’s took the first penalty of the game when David Pastrnak punched Anton Lundell at a stoppage in front of Jeremy Swayman. The B’s killed it off and, when Aaron Ekblad hauled down John Beecher on a rush, the B’s took the lead on the power play, and quickly.

Just eight second after Ekblad took his seat, Jake DeBrusk fed Pastrnak at the right circle and he blasted a one-timer past Sergei Bobrovsky at 8:53. It was the B’s first power-play goal of the series and just Pastrnak’s second PP goal since Jan. 25.

The B’s took a 2-0 lead at 15:12 on Brandon Carlo’s third goal of the playoffs. With the B’s pressuring, the puck looked like it was going to get out of the zone but Carlo caught up to and flung it toward the net, beating Bobrovsky.

Pat Maroon also made his presence felt. In warmups, he had been barking at Bobrovsky. And in the first period, he appeared to be offering out both Bennett and Matthew Tkachuk, delighting the vengeance-minded crowd. Neither Panther took him up on the offer. Even Swayman got in on the act, giving Tkachuk a tap and giving him a “let’s go” gesture with his glove.

This is not to say that the B’s dominated the first period. Quite the contrary. They again were outshot 15 -5 and Swayman had to be sharp. His best save came on an early Vladimir Tarasenko breakaway.

The B’s had a couple of chances to stretch the lead to three goals in the second period, including a two off the stick of Charlie Coyle.

Swayman had been airtight for the first half of the game, but Anton Lundell sneaked one by him on what looked like a nothing play at 14:51, beating him on a shortside shot from the left circle, one-timing an Evan Rodrigues pass from below the goal line.

That seemed to rattle the B’s a bit and Gustav Forsling nearly tied it shortly after the Lundell goal and he hit the crossbar with a blue line that Swayman appeared not to pick up.

Before the period was out, the B’s had a huge opportunity to retake their two-goal lead when DeBrusk had a clean break-in but his backhander went between Bobrovsky’s pads and just wide.

The B’s had 20 minutes to protect a one-goal lead. They didn’t come close to making it, and the turn of events infuriated the fans.

Hampus Lindholm was called for an early interference penalty and it looked like the B’s were going to kill it. But with two seconds left, Bennett got away with another one.

In a scramble in front of the net, Bennett crosschecked Coyle from behind into Swayman. Bennett then tapped it into the open net in front of him at 3:41.

Coach Jim Montgomery challenged for goalie interference – the rule states that if a defending player is “pushed, shoved or fouled” so as to cause the defending player to come into contact with his own goalkeeper…it would be disallowed” – but the goal was stunningly allowed to stand, turning an apoplectic Montgomery’s face a beet red.

The B’s killed the ensuing penalty, but they couldn’t change the tide. Sasha Barkov gave the Panthers a 3-2 lead at 7:31 as he cut through the slot and several Bruins to beat Swayman over the blocker.

The B’s did get a late PP but they were far too tentative for what was at stake. With Swayman pulled in the final minute, the B’s got anotrher power play and McAvoy had chance from the slot but Bobrovsky made a great stop to save the game for Florida.