WASHINGTON — For a franchise as familiar with calamity as the Islanders, Monday may end up ranking awfully high on the list. 

The Islanders’ playoff fate fell out of their own hands with an 5-2 blowout loss to the Capitals in which they were about as close to winning as Charlie Brown was to kicking the football.

The loss does not eliminate the Isles from playoff contention, but it does amount to inviting the Penguins to hop them in the standings. 

Pittsburgh, which did not play Monday, finishes its season with games against the bottom-feeding Blackhawks and Blue Jackets and now controls its own destiny.

So, too, do the Panthers, who moved a point ahead of the Islanders with an overtime loss to Toronto, but — in what somehow counted as optimism — lost on a John Tavares overtime winner, of all things, which kept alive the Isles’ chances of passing Florida should the Panthers lose to Carolina on Thursday. 

The Islanders will not only need to beat Montreal on Wednesday, but hope that one of the two squads tanking for Connor Bedard pulls off a massive upset in order to get them into the playoffs. 

Otherwise, add this game to the list of embarrassments with which the generation of Islanders fans too young to have seen the Dynasty is all too familiar.

Really, add the last 10 days, in which the Islanders have dropped three of five games in regulation to allow Florida and Pittsburgh the inside track to two wild-card spots over which the Isles held pole position entering April. 

The Capitals, who played without seven skaters including Alex Ovechkin and T.J. Oshie on Monday, scored their first goal within 36 seconds of puck drop and their second within 1:03.

Shell-shocked and rattled, the Islanders would only recover enough to force Darcy Kuemper into a few acrobatic saves on a night in which he finished with 38 total and easily outplayed Ilya Sorokin. 

The lack of intensity from the Islanders, for a game in which their season was on the line, was nothing short of staggering.

Their defensive-zone play was something out of a blooper reel.

The forecheck was nonexistent. T

he power play, dysfunctional all season, did not suddenly turn a page in Game 81, earning just one shot on net in 6:00.

As they have so many times this season, the Islanders played down to an inferior opponent. 

It is not just Monday, but the accumulation of those games that could now cost them a playoff spot. 

It was a mess of a start for the Islanders, but particularly so within their own zone.

Dylan Strome took advantage of a giveaway from Adam Pelech to lash a right-circle wrist shot past Sorokin to open the scoring.

Just 27 seconds later, Rasmus Sandin beat Sorokin on a seemingly harmless look from the opposite circle. 

Craig Smith would add a third Capitals goal before the first period mercifully ended, getting the better of Sorokin on a blocker-side look after the Islanders again made a mess of things within the defensive zone. 

Over the ensuing 47:47, the Islanders got their fair share of chances but could not finish enough of them.

That included, but was not limited to, a Jean-Gabriel Pageau slap shot all alone in the slot, a three-on-one in which Pierre Engvall fumbled away a pass to Kyle Palmieri and a trio of Kuemper saves coming on Bo Horvat twice before the kicker on Anders Lee’s backhand. 

By the time Hudson Fasching scored with 5:08 to go, it was enough to set off a scrambling finish that included goals from Tom Wilson, Casey Cizikas and Strome that proved only to inflate the final scoreline. 

To lose a playoff spot — one their chances of securing were north of 90 percent just 10 days ago — would represent a catastrophe for an organization that believes itself to be within a window of contention.

If the Islanders miss the playoffs for the second straight season, that belief would strain reality. 

Last season, the Islanders could fall back on a series of disasters outside their control to explain away a disappointment. 

This time around, there would be nowhere to look but the mirror for everyone in the organization.