You need good goaltending for a playoff run, Jack Capuano said. You need luck, you need health and you need special teams. “And we haven’t had the luck or the health,” he said.

On Saturday afternoon, you could add special teams to the list. Throw goaltending in there, too, while you’re at it.

In possibly their biggest game of the season, the Islanders put on a display that John Tavares called “embarrassing” and “unacceptable,” allowing a shorthanded goal and two power- play goals en route to a 5-0 drubbing by the Penguins at Barclays Center.

This, with rookie Matt Murray (24 saves) in the crease for the Penguins, who announced Saturday that Marc-Andre Fleury will be out indefinitely with his second concussion of the season.

The Penguins, in second place in the Metropolitan Division, clinched a playoff spot with the win and are five points up on the fourth-place Islanders. The Isles have a game in hand but have yet to punch their playoff ticket.

“It’s just frustrating,” Frans Nielsen said. “It should not happen this time of year. I guess you can say I’m a little worried . . . We played well in the first period but then they got a power-play goal and for some reason, we just stopped doing what we were doing. It can’t happen this time of year. I know it happens sometimes, but this time of year? No.”

advertisement | advertise on newsday

Goalie J-F Berube struggled despite handling the Penguins fairly well just 2 1⁄2 weeks ago. He allowed all five goals on 33 shots.

Berube essentially gifted Oskar Sundqvist his first career tally 12:41 into the game when he tried to toss the puck to Nick Leddy and turned it over instead. Sundqvist collected it in the high slot and rattled off a shot past the unprepared Berube for a shorthanded goal.

Midway through the second period, with Nikolay Kulemin in the box for slashing, Patric Hornqvist tipped in a slap shot by Justin Schultz. Sidney Crosby got the second assist on the goal, the 600th of his career.

Phil Kessel scored a power-play goal with 9:20 left in the third period for a 4-0 lead and his 10th point in five games.

“Certain guys feel that other guys can pick it up,” Capuano said. “I don’t think our secondary guys right now are doing anything to help us win, and the older veteran guys feel that in a way, but there’s still a lot of believability and trust in the room.”

This was the Islanders’ first game without defenseman Travis Hamonic (lower body), and they’ve been without goalie Jaroslav Halak since he injured his groin on March 8. Of course, the Penguins were without their goalie and have been playing without Evgeni Malkin, who isn’t expected to return until the playoffs.

“It’s embarrassing,” Tavares said. “It’s a big game . . . [and] it’s unacceptable. It’s going to sting over the next day and a half, so we have to be motivated after this one.”

They’ll need to turn it around quickly, though, because things don’t get easier. The Islanders have a back-to-back on Monday and Tuesday, at home against the Lightning and away against the Capitals.

“We had our chances in the first period,” Kyle Okposo said in a muted, quickly vacated locker room. “It would have been nice to bury some of those . . . We just didn’t play well enough to win.”