MONTREAL — The Islanders keep losing the kinds of games a team just can’t lose. 

It’s not just their 4-3 overtime loss Saturday to the last-place Canadiens, courtesy of Mike Matheson’s game-winning goal, it’s the pile of bad losses before this one. The Islanders have lost twice this season to the Coyotes and Predators, dropped games to the Senators, Flyers and Blues, and on Thursday, they blew a lead at home to the Canucks. Now they can add this one to the list of gimme points lost, which are creeping up on 20. 

Every team is expected to have a hiccup or two, but losses like this are what separates the Islanders, who are still on the outside of the playoff picture, from the teams ahead of them. They can’t win the games that should be simple victories. 

The loss Saturday followed an all-too-familiar script of the Islanders playing down to their opponents, failing to establish themselves early, struggling to break the puck out and failing to hang onto a lead. 

“We gotta find a better way to stay on our toes and play more aggressive when we have the lead,” Ryan Pulock told The Post. “Seemed to get caught a little sitting back and it’s costing us.” 

Twice in the third period the Islanders had a lead, and twice they let the Canadiens tie the score. 

First, after Bo Horvat’s power-play goal put the Islanders ahead 2-1 with five seconds to go in the second period, Justin Barron tied the score for Montreal just 4:02 into the third. Barron took Evgenii Dadonov’s feed off the rush and fired it past Semyon Varlamov for his first goal of the season. 

Then, after Matt Martin put the Islanders back in front, redirecting Alexander Romanov’s point shot at 10:54 of the third, Kirby Dach came back to tip in Mike Matheson’s shot with 3:16 to go in the game. 

In overtime, the Islanders had a golden chance to win it after Mike Hoffman was called for slashing, but thanks to strong goaltending from Sam Montembeault, who finished with 27 saves, they could not. Then they lost Hoffman coming out of the box, and he fed Matheson for the winner, which stood after a lengthy review for offside. 

“It’s extremely deflating,” Islanders coach Lane Lambert said. 

As for the goal? 

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

The Canadiens struck first, as Nick Suzuki sent Rafael Harvey-Pinard’s backdoor feed into an open Islanders net 12:57 into the first. Brock Nelson tied it just over two minutes later, when he redirected Noah Dobson’s shot past Montembault. 

Horvat, who threw a puck at the net from below the goal line, which Montembault mishandled, for his third goal in four games, gave the Islanders the lead late in a second period in which they were largely outplayed. 

All the Islanders had to do was close it out against a team that had been outscored 50-72 in third periods going into Saturday. 

They couldn’t. 

“When you have the lead in the third, we gotta find a way to lock that down,” Pulock said. “It doesn’t matter who you’re playing against. You gotta find a way to win those when you have a lead.” 

Now that the Islanders have lost two straight games to teams below .500, all the momentum from a four-game winning streak and trading for Horvat is gone. They still have a chance to go on a run, but they are clinging to the outer edges of the playoff conversation and just blew two straight third period leads. 

“Gotta do a better job, especially playing with the lead,” Dobson said. “We gotta be smarter in the way we manage pucks, closing quicker on guys. Think we gave them a little too much time and space to get some movement. Obviously that wasn’t enough.” 

Gotta be smarter. Gotta be better. Gotta be a whole lot of things, otherwise the Islanders will be spending their second straight summer on the golf course.