The Islanders had given up a lead they held entering the third period the past two games. They were in the same position on Tuesday night, up by a goal after 40 minutes, but this time they were consistent and aggressive.

And ultimately triumphant. A 2-1 lead quickly became 4-1 and led to a 4-2 win over the Blue Jackets at Barclays Center, as structurally sound a game as the Islanders have played all season as they moved to 3-0-1 under Doug Weight.

The Isles chased Sergei Bobrovsky on Jason Chimera’s goal at 5:21 of the third, one that followed Brock Nelson’s first goal in 10 games just 35 seconds into the final period. The Isles held a dangerous Columbus team to just 16 shots on goal until a flurry in the closing minutes got the visitors’ total to 23, tying a season low against for the Islanders.

“We looked like a confident team that has something to prove and somewhere to go,” Weight said. “Top to bottom, one of our best efforts of the year.”

And it came after a slow start. Neither team generated much and Columbus took the lead on Nick Foligno’s goal from in tight after Ryan Murray’s slapper caromed off Nick Leddy and crawled over Thomas Greiss’ shoulder where Foligno swept it in at 8:55.

The Islanders had just one shot on Bobrovsky to that point, but they were able to start tilting things back during a first-period power play. And the second was likely the Isles’ best period of the season, with the Blue Jackets spending precious little time in the Islanders end while a four-line rotation hemmed Columbus in its own zone.

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And that was without Anders Lee (illness) and Anthony Beauvillier (foot), two regulars who can generate off the forecheck.

“We didn’t make a major change (to our structure), but our D and centermen are key in our own end,” said Josh Bailey, who banked a centering feed off Seth Jones’ skate to tie the game at 1-1 for his 100th NHL goal at 2:21 of the second. “Our D did a great job for us tonight. They were in and out of our zone quick.”

Nikolay Kulemin got the call to fill Lee’s spot on the top line with Bailey and John Tavares and he was effective against the Blue Jackets’ heavy lineup. Kulemin had position on Jones for Bailey’s goal, then Kulemin got his own from the doorstep at 16:29 of the second after Calvin de Haan’s shot hit Tavares’ leg and sat down on Kulemin’s stick.

That 2-1 lead had quickly turned to 2-2 both Saturday against the Kings and Sunday against the Flyers, with the Isles splitting the games and taking three of four points. There was no letup on Tuesday, at least on the home side — Columbus is now 6-6-3 since its 16-game win streak ended.

“It was huge we didn’t sit back in the third,” said Nelson, who had two good chances in the first period that Bobrovsky denied and looked to the ceiling in relief after snapping one home. “We took away their time and space well throughout.”

Chimera picked off a lazy pass and snapped one by Bobrovsky to seal it and give the Islanders a huge boost. They host the Canadiens on Thursday, the last game before the All-Star break, and they are feeling better about themselves than at any point this season.

“At this point in the year you’re not always feeling your best,” said Tavares, who had two assists. “It’s a big win and we’ve got to carry it through to the break.”