PITTSBURGH — This wasn’t a throwback to the bad old days of a few years ago, when Sidney Crosby and the Penguins dominated the Islanders.

But this was an ugly game for the Isles, who gave up a pair of power-play goals by Crosby and a shorthanded goal in a 5-2 loss Saturday night.

It was 5-0 in the second period just after Thomas Greiss got the mercy pull from the net and rookie Christopher Gibson stepped in to make his NHL debut.

“They’re an opportunistic team,” Calvin de Haan said. “We gave them a couple power plays and they capitalized.”

The Islanders were sluggish out of the gate, right from a few seconds in, when Crosby pounced on a mishandled puck and forced Greiss to make a good save. Phil Kessel chipped one past Greiss at 3:34 and the Islanders handed the Penguins two power plays later in the period. De Haan was whistled for delay of game and Anders Lee was called for a soft holding minor on Trevor Daley in the Pittsburgh end.

Crosby misfired on a rebound to Greiss’ left about half a minute before he roofed a rebound at 16:35, part of a 20-shot first period for the Penguins. The Islanders had some offensive zone time midway through the first, but as happened in Buffalo two nights earlier, penalties stunted any consistency.

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“You’ve got 87 , 71 [Evgeni Malkin, three assists], 58 Kris Letang, three assists] roaming around on the power play, you can’t give them opportunities,” coach Jack Capuano said.

Another borderline call, this one a boarding minor to Matt Martin, put the Penguins back on the power play midway through the second after the Islanders began to generate some momentum and put a little pressure on Marc-Andre Fleury, playing for the first time since Dec. 14 because of a concussion.

Crosby whipped a wrist shot past Greiss at 10:25. Given their first power play 14 seconds later, the Islanders gave up a two-on-one and Matt Cullen snapped a shot past Greiss at 10:57, prompting the call to Gibson.

“We weren’t doing anything to help him,” Capuano said of Greiss, who faced 26 shots in barely half a game.

Patric Hornqvist’s mid-air deflection over Gibson’s shoulder made it 5-0 at 14:40. John Tavares scored 39 seconds later and Nick Leddy beat Fleury with 56.3 seconds to play, giving the impression that the Isles simply tidied up the final result in garbage time. They did throw 40 shots on Fleury, however.

“You might think I’m crazy, but it didn’t feel like a 5-2 game,” de Haan said. “Yeah, we could obviously play better, but we did some good things, too.”

It didn’t help that this was the Isles’ first game without Johnny Boychuk, sidelined indefinitely with a shoulder injury. The penalty kill had its success streak snapped at 42 in the third period in Buffalo on Thursday, and now they’ve allowed three goals in the last five times short.

The Isles also lost Cal Clutterbuck to an upper-body injury in the first period. He tried to return in the second but didn’t last a full shift.

Notes & quotes: Gibson made 16 saves in his NHL debut. “I was pretty nervous at the beginning. Even Crosby came up to congratulate me on my first game,” Gibson said . . . Jaroslav Halak (upper body) skated yesterday morning and might make his return today against Dallas at Barclays Center. If that happens, Gibson will go back to Bridgeport.