Henrik Lundqvist of the Rangers reacts as Max Pacioretty of the...

Henrik Lundqvist of the Rangers reacts as Max Pacioretty of the Golden Knights celebrates his second-period power play goal with his teammates at Madison Square Garden on Monday. Credit: Jim McIsaac

Rangers coach David Quinn said it, after that wild comeback win in Montreal a couple weekends ago: When the Rangers are good, they’re good. And when they stink, boy, do they stink.

Playing their third game in four nights Monday at the Garden against the Vegas Golden Knights, let’s just say the Rangers weren’t good.

They started poorly; their power play struggled (0-for-6); their penalty kill struggled (0-for-2). And the end result was an unsightly 4-1 loss to the Knights that ended a five-game point-earning streak.

“We’ve either been good, or really bad,’’ Quinn said after his team fell to 13-10-3 on the season. “And, you know, it’s a mindset. It’s something we’ve got to completely buy into: that night in, night out, we’ve got to be way more committed to playing the right way, and playing defense. And, you know, I didn’t think our ‘D’ corps was really all in from a defending standpoint. I thought we were way too offensive-driven.’’

With backup goalie Malcolm Subban playing while No. 1 Marc Andre Fleury is away from the team after the death of his father, Vegas jumped on the Rangers early, with two goals by Alex Tuch giving them a 2-0 lead before the game was four minutes old.

The first goal was the result of a goaltending error by Henrik Lundqvist, who stopped, but failed to catch Tuch’s shot from the left wing. As the puck lay on the ice, just outside the goal line, and players all around him scrambled to try and get it, Lundqvist swung his body around, to try and cover it up. But all he did was knock the puck over the goal line with his pad to give Vegas the lead, 1-0, at 1:34 of the first period. It was reminiscent of the first goal Lundqvist allowed in the overtime loss Friday in Boston, when the puck hit the post and Lundqvist knocked the rebound in with his stick, as he tried to cover it.

Vegas made it 2-0 with a power play goal from Tuch, who tapped in a pass from Nate Schmidt at the back post, just two seconds before a holding the stick penalty to Brady Skjei was set to expire.

The Rangers, who were being outshot, 13-2 at one point in the first period, seemed to stabilize and stop the bleeding the rest of the way, and by the end of the period, they were within 17-12 on the shot clock, and they were about to start the second period with 1:14 left on a power play after Nicolas Roy got penalized for shooting the puck over the glass.

But the power play ended without a goal, and shortly thereafter, a shot attempt by Skjei was blocked and Vegas forward Reilly Smith – younger brother of the Rangers’ Brendan Smith – scooped up the rebound and went the distance on a breakaway, going to his backhand to beat Lundqvist for his 12th goal of the season, at 4:44 of the second.

Quinn called that goal “a gift,’’ and that was the one, he believed, that killed the Rangers. It was also the one that bothered Lundqvist (28 saves) the most.

“Of all the goals, I felt like that was probably the one I had the biggest chance to stop,’’ Lundqvist said. “[Smith] made a good move, but at the same time, as a goalie, one-on-one, you want to come up with the save.’’

Fifteen seconds after that goal, Kaapo Kakko was sent off for a high sticking penalty, and Vegas cashed in on the power play, with Max Pacioretty hammering home a one-timer from the right circle for his 10th goal of the year, at 6:20.

Brendan Lemieux broke the shutout when he deflected Jacob Trouba’s shot past Subban at 15:15 of the second period. But unlike in Montreal two Saturdays ago, when the Rangers rallied from 4-0 down to win, 6-5, they weren’t coming all the way back this time.

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