By Michael Hurley, CBS Boston

BOSTON (CBS) — Seven-game playoff series are long. At least, in theory. Really, though, so much of the composition of these series is determined by what takes place in the matter of a few instants.

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One sequence that spans mere minutes can oftentimes be the difference between a grinding seven-game series and, say, a speedy five-game affair.

It appears as though the Bruins just authored one such moment.

It came some seven minutes into the third period in Monday night’s Game 4 against the Carolina Hurricanes. Through 40 minutes, it quite simply was not Boston’s night. Goaltender Jaroslav Halak, two days removed from an inspired performance after being thrust into the starting position, allowed two goals that would be considered on the weaker side. The offense had gone cold, with skaters failing to finish the few chances they did manage to generate. Even the physical part of the Bruins’ game was more or less missing on this night.

And so, with 20 minutes left to play, all Carolina had to do was play it safe and hold the lead, and they’d have themselves a 2-2 series. Yet seemingly out of nowhere, the Bruins erupted, pouring four goals past James Reimer in less than seven minutes — after Reimer had allowed just two goals in his previous 100-plus minutes on the ice in the series.

It began when Jake DeBrusk simply outhustled everyone in a black and red jersey. The winger, who’s had trouble finding his game in Toronto, spun defenseman Haydn Fleury at the Carolina blue line and found himself in a desperate footrace against Reimer. The goaltender came charging out of his net, but DeBrusk got to the puck first. Reimer made a last-ditch effort to take out DeBrusk, which did work … but not before DeBrusk calmly sent the puck toward the open cage while crashing to the ice.

Jake DeBrusk slides to the corner after scoring a goal past James Reimer. (Photo by Elsa/Getty Images)

Having cut the Hurricanes’ lead in half, the Bruins knew they were one play away from evening the game — and potentially wrecking the series for Carolina.

That play came from a place you don’t often see in the NHL these days: A big, heavy, thunderous, and downright brutal body check in the offensive zone.

In this case, it came from Charlie McAvoy, and it sent Jordan Staal into the air and promptly out of the game.

Bruins head coach Bruce Cassidy said that hit did help lift his team, but the bigger effect was likely a negative one for Carolina.

“The McAvoy hit — I think we were playing and we were gonna push and we were pushing. So obviously it helps us a lot, but I think it really demoralizes the other team when one of your veteran players, a leader in your room, a really respected player in the league takes a good, hard, clean hit. It affects your group,” Cassidy said. “It affected us positively and probably them in a negative manner.”

Without 18,000 fans in attendance to react to such a moment, DeBrusk said he didn’t even get to see the hit. His teammates’ reaction, though, let him know it was a big one.

“He’s got a lot of meat over there,” DeBrusk said of McAvoy. “I didn’t actually see the hit live, but like you said, the reaction of the bench. Any time — it’s so weird without fans, to be honest with you. Any time there’s a big play or a good scoring chance, the only way you know is by the bench reaction. Obviously, it was a big hit and it was a good moment for us. That’s when we’re coming hard.”

It wasn’t entirely clear in the moment whether that energy would transfer to McAvoy’s teammates. It didn’t take long to learn the answer.

Just 17 seconds after the McAvoy hit, Joakim Nordstrom confidently carried the puck behind the Carolina net and sent a pass through the right faceoff circle to Connor Clifton — a play not at all dissimilar to the one that led to Dougie Hamilton’s goal to help beat the Bruins in Game 2.

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Clifton delivered the game-tying goal, and from there, the Bruins were off to the races.

Just 90 seconds after the Clifton goal, Brad Marchand broke free for a breakway, thanks to a brilliant indirect pass from Torey Krug. Based solely on his reaction after slipping the puck through Reimer’s exposed five-hole, you never could have known that Marchand was playing this game in an empty arena.

Brad Marchand (Photo by Elsa/Getty Images)

The Bruins poured it on with a fourth goal — DeBrusk’s second — less than three minutes later. It appeared at the time to potentially be excessive, but after Carolina scored a goal with their goalie pulled in the final minutes, that fourth and final goal proved to be the game-winner.

Cassidy said the coaching staff offered some tactical advice to players during the second intermission, when the team was down 2-0. But there was no rah-rah speech; all of that fire came simply from playing better and finishing chances.

“Just stay in the game, keep playing, maybe you know push the envelope a little offensively,” Cassidy said of his between-periods message. “You’re down a couple, having trouble scoring so you’re not going to go out there and gamble, but you need to be proactive offensively and it worked out in our favor.”

Though an open-ice hit doesn’t directly put the puck into the net, McAvoy knew that the body contact he cleanly delivered could be the type of difference-making play it ended up being.

“You have to be able to create your own energy on the bench,” McAvoy said. “And going into that third period, obviously you’re down two and the game hadn’t really been in our favor. We had some chances and stuff but we were looking to create some energy and that was kind of the message — that we weren’t out of it. It was opportunity to step up and make a hit, try and separate a man from the puck. We were already playing well. And just to see so many guys step up and make tremendous plays tonight when it really mattered to get us a win was just so awesome to see. It really lifts the spirit of the team.”

While the hit was huge, Marchand credited DeBrusk’s first goal — an all-out, individual effort — for getting the ball rolling in the right direction for his team.

“After that first one, we start to roll and we got a ton of life,” Marchand said. “Any time you have life, it’s a dangerous thing. You can feed off it. Again, especially with our group, the way that we play and the emotion and character that we have, it’s when we’re at our best.”

As a result of that massive swing in a seven-minute span, the shape of the entire series changed significantly. Instead of a 2-2 series with two teams bearing down for a long fight, the Hurricanes will be facing elimination the next time they take the ice. Had Carolina won the game, history dictates that they’d have roughly a 47.5 percent chance of winning the series. Now facing a 3-1 deficit, their historical chances are at 10.2 percent.

Canes head coach Rod Brind’Amour summed it all up succinctly.

“They threw everything at us and we didn’t have an answer,” Brind’Amour side. “It was tough to watch, that’s for sure.”

Brind’Amour added: “We just sat back and we let them take it to us. And, you know, that’s what championship teams do. They take it to you.”

The events of Monday night were merely a reminder that there’s never a good time to get comfortable in the Stanley Cup Playoffs. Even the safest of leads and the surest of outcomes can be shattered by a sudden goal, a devastating hit, and a team that knows how to properly channel emotions in the biggest moments of the biggest games.

Brad Marchand is congratulated by teammates after scoring the go-ahead goal in Game 4 against the Carolina Hurricanes. (Photo by Elsa/Getty Images)

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You can email Michael Hurley or find him on Twitter @michaelFhurley.