Islanders goaltender Semyon Varlamov is scored on by the Canadiens'...

Islanders goaltender Semyon Varlamov is scored on by the Canadiens' Nick Suzuki (not shown) as Islanders' Ryan Pulock defends during the first period of an NHL game in Montreal on Saturday. Credit: The Canadian Pressvia AP/Graham Hughes

MONTREAL — The Islanders know how to take a lead. They just don’t know how to hold it, to misquote famed comedian Jerry Seinfeld.

But two straight blown opportunities against two NHL also-rans is no laughing matter, given the Islanders’ precarious position as they fight to return to the NHL playoffs after last season’s absence.

“It’s two leads blown the last couple of games in the third period,” defenseman Noah Dobson said. “We usually know how to lock it down. We’ve just got to do a better job. Careless with the puck a little bit.”

Two one-goal leads were wasted in a 4-3 overtime loss to the Canadiens on Saturday afternoon at Bell Centre. The Islanders couldn’t convert on an overtime power-play chance before defenseman Mike Matheson along with Mike Hoffman coming out of the penalty box slipped behind the defense for the winner at 4:38 of the extra period. Matheson’s goal survived a lengthy video review for offside.

The Islanders (27-23-6) also couldn’t hold a two-goal lead in Thursday night’s 6-5 loss to the Canucks at UBS Arena. The Penguins and Capitals, ahead of the Islanders in the Eastern Conference wild-card race, have played four and two fewer games, respectively.

The Islanders are 4-2-3 in their last nine games when they’ve held the lead through two periods. Overall, they are 19-3-3 when leading after two periods. Those lost nine points are the most in the NHL, according to team statistician Eric Hornick.

“Maybe in the third period, we came out a little flat and didn’t have enough push in the last game,” said Bo Horvat, who scored in his third straight game as his tip of Dobson’s shot gave the Islanders a 2-1 lead at 19:55 of the second period. “But today, I thought we had our chances and still came up strong. But we just couldn’t get it done.”

Defenseman Justin Barron beat Semyon Varlamov (27 saves) with a wrist shot from the high slot at 4:02 of the third period to tie the score at 2-2.

Matt Martin regained the lead for the Islanders when he deflected defenseman Alexander Romanov’s shot from the left point at 10:54. But the Canadiens tied it again as Kirby Dach tipped Matheson’s shot at 16:44.

“We had two leads in the third period that we didn’t hold,” coach Lane Lambert said. “There’s a certain point in time where, as an individual, you have to win a battle. When that doesn’t happen, you decrease your chances of holding that lead.”

Lambert was displeased with the Islanders’ structure on Matheson’s overtime winner.

The Islanders had generated two power-play shots and had three other attempts blocked while skating four-on-three after Hoffman was called for slashing defenseman Sebastian Aho at 2:29 of overtime.

But Hoffman popped out of the box and pushed the puck forward to Matheson as Mathew Barzal, Jean-Gabriel Pageau and Zach Parise were caught up ice, with only defenseman Adam Pelech getting back. Barzal’s turnover started it all.

“It’s a lot of situational awareness,” Lambert said.

Nick Suzuki gave the Canadiens a 1-0 lead at 12:57 of the first period as he wound up open to Varlamov’s right for Rafael Harvey-Pinard’s quick feed.

Brock Nelson extended his career-high point streak to 10 games, deflecting Dobson’s blue-line feed to tie it at 1-1 at 15:01 of the first period.

The Canadiens (21-27-4), who got 27 saves from Sam Montembeault, were playing their first game in 11 days after their All-Star break/bye week.

Said Martin, “We’ve still got to find a way at the end of the day to come away with two points we really need.”

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