John Tavares of the Islanders celebrates his second-period goal against...

John Tavares of the Islanders celebrates his second-period goal against the Rangers at Madison Square Garden on Tuesday, Oct. 14, 2014. Credit: Jim McIsaac

The odds are pretty long that the Islanders won't be 20-0 by Thanksgiving. But in their toughest test of the young season, they rose to 3-0, scoring four goals in the third period en route to a 6-3 defeat of Henrik Lundqvist and the rival Rangers at Madison Square Garden last night.

While there is joy in Islanders territory, there is trouble in Rangerland. It was the Blueshirts' second consecutive meltdown and third consecutive loss after edging the Blues in St. Louis on Oct. 9. They stand at 1-3 and have allowed 17 goals in those three losses.

On Sunday, the Rangers surrendered five goals in the second period to the Maple Leafs. "It's about ten minutes in the last two games that somehow we became unraveled on the ice," coach Alain Vigneault said. "I'm sure we can fix that."

That may be easier said than done. Dan Girardi called the third period "a nightmare snowball effect" that buried the Rangers.

On goals by Rick Nash and Derick Brassard, the Rangers had leads of 1-0 and 2-1 but the Islanders came back each time.

The second rally came at 15:03 of the second -- which the Rangers had dominated, outshooting the Isles 21-8 -- after a behind-the-net turnover by Michael Kostka, playing his first game after being called up for the injured Dan Boyle. Nikolay Kulemin found John Tavares alone in front.

"I really liked our first 40 minutes five-on-five," Vigneault said. "Problem was, in the second we had numerous Grade A opportunities, couldn't score, then we made a few mistakes and they made us pay."

With the score tied at 2, the Isles scored three in the first 5:20 of the third and another on Nick Leddy's 60-foot slap shot at 10:59. Kyle Okposo scored 48 seconds into the period after another bad turnover by Kostka, this time in front. Brock Nelson buried a pass at 4:50 and Mikhail Grabovski's pass was deflected by Kevin Klein's raised stick past Lundqvist.

"We were having a strong game, but we started making some mistakes in our own end, and I'm not able to stop those right now," Lundqvist said. "I lose my structure when we as a group lose our structure . . . but it's my job to be there and take care of the mistakes. When we lose our structure a little bit, I tend to do a little too much sometimes. So I need to keep my patience as well."

At the other end, Jaroslav Halak made 40 saves, facing 21 shots in the second period and allowing only a goal from Brassard, who darted to the net to convert Chris Kreider's pass from behind Halak at 3:50.

In the first period, the Islanders converted their fifth power play in nine attempts when Johnny Boychuk's right point rocket eluded Lundqvist at 10:31. Rick Nash's harmless backhander had slid through Halak's legs at the right post at 6:21. Nash became the first Ranger to ever score a goal in each of his first four games of a season. Nash collected his NHL-leading sixth, of the team's 11, with 2:10 left in the game.

"We have to help our goalie out more than we've been doing. We are letting guys get to the middle and get great opportunities," Nash said. "We're aware of how serious it is. We have to correct our game and get a win on Thursday."

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