WASHINGTON — You’d call it a Thanksgiving hangover, except this is who the Islanders have been all year round.

Which leads you to conclude: Maybe this is who the Islanders are.

Twenty-four games into the season, it’s no longer early, and the Islanders can’t lay claim to playing a decent hockey game in every area except the final score on Friday in Washington. 

Rather, the latest third-period implosion, which led to a 5-4 overtime loss to the Capitals put into a starker reality that the Islanders are not merely behind the league’s typical Cup contenders, but another club which has been accused of hanging on to a core too long, and this without the injured Alex Ovechkin on the ice.

“Can I plead the fifth?” coach Patrick Roy asked wryly to start his press conference. “Maybe I should.”

Outplayed for much of an afternoon that ended on Jakob Chuychrun’s game-winner, the Islanders used a fortuitous series of events — a successful challenge, a rare successful penalty kill and two goals from the ensuing momentum — to snare a 4-2 lead going into the third.

It seemed like real momentum.

It was just as fake as all the other leads the Islanders have let go to waste this season.

Anders Lee took a penalty for hooking just five seconds into the third period and the kill — which had come up huge in the second — faltered, with Dylan Strome wristing one past Semyon Varlamov to cut the lead in half.

The Islanders could not even get to the halfway point of the period ahead, with Tom Wilson taking advantage of a failed clearance by Noah Dobson to rocket in a one-timer off Trevor van Riemsdyk’s feed to tie the game at the 7:24 mark.

The Islanders had a chance to retake the lead after Nic Dowd was called for slashing with 3:50 to go in regulation, but came up empty for the third time of the afternoon on the power play.

That sent the game to overtime, which at least gave the Islanders a point, but there is zero moral solace in watching the Capitals spill off their bench to celebrate Chychrun’s three-on-three winner.

Afterward, Roy pointed the finger at the power play, which he called “awful,” while Lee said he “had two players on the other team telling me how bad of a call that is,” about his own penalty. It was Simon Holmstrom, though, who broke the omerta to state what is, at this point, a pretty obvious — though usually unacknowledged — fact.

“Right now, it’s probably in our head a little bit,” he said. “Even if we don’t want it to be.”

Much as the Islanders deny it, that seems as clear-cut as can be. Though no one is denying Roy’s assertion that they will not win games without a competent power play.

“Our power play’s gonna have to be better than this,” Roy said. “There’s no doubt about it. We’ve been trying all kinds of scenarios but tonight, it was a night they had to come up for us and they had to win the game for us. They had it with three minutes left in the game to be the difference-maker.”

The club will almost assuredly wait and see what they can do when healthy before making a decision on whether to buy or sell, but right now, they are two games behind the very modest goal articulated by Roy on Wednesday night of being NHL-.500 when the reinforcements come in.

Where the Islanders could at least hang their hats on playing a strong game and generating good chances in a lot of prior losses, that was not the case in this one.

It was instead the Capitals who played up ice and who owned the puck, buoyed by a forecheck the Islanders could not solve and defensive-zone breakdowns the Islanders could not afford.

Holmstrom, who played in place of J-G Pageau on the top line after Pageau was made a late scratch with a lower-body injury, helped them seize the initiative with an early goal, then made it his first career two-goal game late in the second.

Scott Mayfield also finished the game in the dressing room after taking a Chychrun shot to the face with eight minutes to go, though Roy said he was fine.

The bigger problem than the injuries, though, is the late-game breakdowns that the Islanders cannot seem to get past.

“I think we just shoot ourselves in the foot a lot,” Matt Martin said.

At this point, the Islanders must hope they are running out of bullets.