Only 14 seconds into the third period Tuesday night, when the Islanders’ Adam Pelech snapped a wrist shot past Igor Shesterkin for a goal, it became clear.

It didn’t matter that the Islanders had been outplayed through 40 minutes. It didn’t matter that they had taken four penalties and given up two power-play goals and taken a two-goal deficit into the visiting locker room at Madison Square Garden. They were right in the match.

And 19:46 later, they walked back up the tunnel as 4-3 winners over the Rangers, another comeback victory, and one that clinched the season series over their crosstown rivals.

Throughout last season, when the Islanders couldn’t seem to string together wins even once they got healthy, they repeated again and again their belief in the group they had. Now, with their record at 9-5-0 and their resiliency on full display after a three-goal third period stunned the Rangers, they are being vindicated.

It is only November. But if their current play is an indicator of how the rest of the season will go, then Oct. 29 — when the Islanders roared back in the third period against the defending-champion Avalanche to win — will be remembered as the turning point. Since then, they’ve done the same thing against the Flames and the Rangers. They also have won seven of their last eight games, dating to the first game against the Rangers on Oct. 26.

The resilience in the room that is defining this Islanders team can be traced on a line straight from the comeback against Colorado to now.

“I would say [that game] felt more like us,” captain Anders Lee said. “We lost a little bit of that last year. A game like that, a game like one of these last two nights felt more like who we are. This is a group that’s done that a lot before. Not as much as we wanted to last year, but in years prior, that’s how we played the game.

“Didn’t matter what the score was, we were gonna put our best effort out there and make something to the best of our abilities happen. I think you’re seeing a few of those instances come to fruition.”

Of course, any team in any sport will always believe it can come back in any game. But it is one thing to believe it and another to be confident in that belief. When they returned to the dressing room for the second intermission on Tuesday after a shambles of a second period, the Islanders were still confident in their belief.

“You’re kinda sitting in the same spot and in here after two periods being like, ‘We can do this,’ ” Matt Martin told The Post. “ ‘We’ve done this before.’ And so with the belief, every time you do it comes confidence, and more confidence can only help. The more confident your group is that they can come back from anything, the better.”

The Rangers, for their part, looked as if they had been hit by an oncoming wave during stretches of the third period. After Brock Nelson tied the score at 3-3 with a power-play goal at 12:46 of the period, it took less than two minutes for Lee to come up with the winner, corralling a rebound from Alexander Romanov off Igor Shesterkin’s pad and in.

“This team’s got it,” Lee said. “And we know what we’re capable of when we play the right way.”

The Islanders, Lee said, need to do more to put together a 60-minute effort and cannot rely on comebacks forever. But it seems possible that a group which seemed destined for a slide into mediocrity a month ago is a sleeping giant ready to wake.

“The identity’s really the same [as two years ago],” Martin said. “There’s a lot of belief in this room right now.”