Rangers goaltender Igor Shesterkin and left wing J.T. Miller react...

Rangers goaltender Igor Shesterkin and left wing J.T. Miller react after Calgary Flames right wing Matt Coronato scored a power-play goal in the first period of an NHL game at Madison Square Garden on Tuesday. Credit: Kathleen Malone-Van Dyke

Of all the awful, inexcusable losses in a confounding season, Tuesday’s 2-1 loss at Madison Square Garden to the struggling Calgary Flames had to be the most unacceptable one yet for the Rangers.

“I would say it’s the most [disappointing],’’ Artemi Panarin said. “But yeah, it’s hard to remember all of them right now, because we have a bunch of them this year . . . We just can’t play like that when we’re fighting for our [playoff] life.’’

Montreal’s 6-3 win over Ottawa knocked the Rangers out of the second wild-card playoff spot in the East. Montreal (33-27-7, 73 points) leapfrogged the Rangers (33-30-6, 72) to take over the spot.

Panarin early goal gave the Rangers the lead 1:13 into the game, but the Flames, playing the second game of a back-to-back, rallied on goals by Nazem Kadri and Long Island product Matt Coronato. They outshot the Rangers 35-13 and held them at bay for the final two periods to deal them their second straight loss.

“They were far faster than us tonight,’’ Panarin said. “We can’t play like that against team who’s playing back to back.’’

Panarin was asked if he thought the Rangers played hard enough.

“It looks like, no,’’ he said. “I’m sure everyone tried. Just sometimes it’s like — I don’t know. It’s hard to say . . . it’s like I say always, like a bunch of things. But we’ve got to be sharper.”

“There was nothing there,’’ Rangers coach Peter Laviolette said of his team’s effort. “They were faster than us. They get to the ice quicker than us. They were more ready.’’

But how? Rangers players have been talking for weeks about how every game they play now is essentially a playoff game. Before the opening faceoff, they held the second wild-card spot by a point over Montreal.

Now they are a point behind the Canadiens, and two ahead of the Islanders, Columbus and Detroit. The Rangers have only 13 games remaining.

With the Flames having played Monday night (a 6-2 loss in Toronto) and starting backup goaltender Dan Vladar, it looked early on like this would be an easy one for the Rangers, especially after Panarin put them ahead with what appeared to be a routine wrist shot that got by Vladar’s glove for Panarin’s seventh goal in 10 games and 30th this season.

But after that, it was the Rangers, not the Flames, who looked like the team playing on the second night of a back-to-back. The Rangers were charged on the official scoresheet with committing 11 giveaways while recording no takeaways in the first period. Calgary was charged with seven giveaways and credited with four takeaways.

Plus, the Flames outshot the Rangers 14-5 in the first period and took a 2-1 lead into intermission on the strength of goals by Kadri and Coronato, a Greenlawn native who scored on the power play with Matt Rempe sitting out an elbowing penalty.

The second period wasn’t much better for the Rangers. They didn’t allow any goals, but they were outshot 10-3 and failed to get a shot on goal on their first power play. At one point they were booed on the power play as they were unable to gain control of the puck and enter the offensive zone with possession. They were booed again at the end of the period.

The Rangers desperately tried in the third period to rally, but they were outshot 11-5 and were it not for the brilliant goaltending of Igor Shesterkin (33 saves), the score would have been a lot worse.

Calgary appeared to score an insurance goal into the empty net with 9.3 seconds remaining, but the Rangers challenged the goal, alleging the play was offside. Video replay showed that it was, and the goal came off the board.