The four points from Plekanec and Kostitsyn gives their line with Michael Cammalleri 25 points in nine games this season. Kostitsyn notched his third straight two-point game and his fourth of the year after getting multiple points in a game only nine times all of last season.
"I don't want to praise our line too much, it's way too early to be too happy about it," Plekanec said. "But things are going well for us."
Travis Moen, Mathieu Darche and Jeff Halpern also scored for the Canadiens (6-2-1), who have one loss in their last six games and kept pace with the Tampa Bay Lightning to stay tied for first in the Eastern Conference.
James Wisniewski had a goal and two assists and John Tavares and Doug Weight also scored for the Islanders (4-3-2), who scored twice on the power play to improve to 13-for-46 with the man advantage this season.
But they have scored only 12 goals playing 5-on-5.
"We didn't skate, we didn't make it harder for the opposition to make questionable decisions with the puck," Islanders coach Scott Gordon said. "If you're going to allow them to make skilled plays all the time, they have some pretty good skill over there and they're going to make them."
Tavares scored his sixth goal in his last five games when he tipped home a Wisniewski point shot to briefly bring the Islanders to within a goal just 13 seconds into the third period.
With three points, Wisniewski leapfrogged past Pittsburgh's Kris Letang and Colorado's John-Michael Liles to take over the League lead amongst defenseman with 11 points.
The Canadiens' power play continued to struggle with an 0-for-3 performance, dropping them to 2-for-32 on the season.
Carey Price made 18 saves as the Canadiens allowed fewer than 30 shots on goal for a sixth straight game. Conversely, Dwayne Roloson made 29 saves as the Islanders gave up at least 30 shots for a fifth straight contest.
"Our guys are playing well offensively and I think that's stemming from playing well defensively," Price said. "That's where we’re getting our chances from, coming back, protecting our house and attacking from there."
Price got his sixth win of the year, just short of half his total from all of last year when he went 13-20-5.
"We've got to make sure that we stay humble," Price said. "We have to keep doing what's making us successful, and that's working hard."
Canadiens rookie defenseman P.K. Subban appeared to be inspired by facing his good buddy Tavares for the first time as a pro, making plays all over the ice.
But the notoriously vocal Subban says he will keep the bragging to a minimum.
"He's got a whole year on me, so I don't know how much I can boast or brag," Subban said. "Maybe a little chirp, but not too much. He's got a whole year on me, a whole lot of wins under his belt and a whole bunch of points, so I can't really say too much."
In one two-minute span in the first period, Subban put on a show on both ends of the ice. First, he spun three times at the offensive blue line to shake Blake Comeau and let go of a shot that was tipped home by Darche at 13:19 of the first. Then he timed his slide perfectly on a 2-on-1 break to block a shot by rookie Matt Martin about a minute later. And finally he got back to poke a puck away from rookie Nino Niederreiter as he was going in alone, something he did again about five minutes into the third.
"Whatever comes my way, I just handle it," Subban said. "Whether it's lots of action, less action, it doesn't matter. I just have to play the game."
Unfortunately for Niederreiter, those two plays were about the only things he did of note in his ninth game of the season as Gordon and Islanders management have to now decide whether or not to send the fifth overall pick in the 2010 Entry Draft back to the Portland Winter Hawks of the Western Hockey League.
"The game had nothing to do with our decision," said Gordon. "We haven't made it yet, but he wasn't going to make or not make our team based on this game."
After Darche scored to put Montreal ahead 1-0, Travis Moen converted a perfect Plekanec feed on a shorthanded 2-on-1 to put the Canadiens up 2-0 at 17:54 of the first. It was Montreal's first shorthanded goal of the season.
Wisniewski scored on the power play just before the end of the first to bring New York to within one, but Plekanec re-established Montreal's two-goal margin by wiring a shot just under the crossbar at 7:33 of the second.
After Tavares scored to open the third to make it 3-2 Montreal, Halpern banked a backhand off Mark Eaton's leg past Roloson at 6:56 of the third for his third goal of the season.
Weight tipped home another Wisniewski point shot at 12:56 of third, but Kostitsyn put it into an empty net at 18:58 of the third for his sixth of the year and his fourth in three games to ice it.