PITTSBURGH — The Islanders spent much of Thursday night looking like they were moving into a new era with both feet.

Ultimately, though, it was old habits that doomed them to a 4-3 loss to the Penguins in their first game of the season.

The penalty kill was a major focus throughout the preseason, yet it fell short by allowing two goals, with the Islanders conceding a third-period winner to Justin Brazeau. Ilya Sorokin was left unprotected in the final 20 minutes, which overshadowed the initial optimism from Matthew Schaefer’s debut.

Schaefer, at a historic moment, became the youngest player to notch a point in his NHL debut. With about 30 family members and friends cheering him on, he had an impressive performance, assisting Jonathan Drouin’s goal 12:02 into the game, and proving in his first regular-season appearance that he belonged on the ice.

In the long run, this is a significant positive, as is the pace with which the Islanders played throughout the night, addressing the need for speed in a team often criticized for its sluggish gameplay.

Still, with the chance to seize a come-from-behind win after Max Shabanov tied the game at three going into the second intermission, the Russian’s first NHL goal coming off a slick assist from Simon Holmstrom, the Islanders could not.

The Penguins poured down pressure early in the third period, but Ilya Sorokin — whose rebound control had looked shaky earlier in the night — stood up to it, making save after save around the crease.

Finally, though, at 14:21 of the third, Sorokin was beaten as Brazeau got around Scott Mayfield and went forehand-to-backhand, putting the Penguins up 4-3.

The Islanders had a chance to re-tie the game shortly thereafter when Adam Pelech drew a hooking call on Ben Kinde with 3:45 to go.

Even after Patrick Roy pulled Ilya Sorokin with a minute to go in the man advantage, though, the Islanders could not come up with a tying goal. Nor could they skating at six-on-five for the remainder, though Drouin came within inches of scoring with 14 seconds to go. Instead of scoring, though, Drouin was assessed a five-minute misconduct major for cross-checking in the scrum that followed the play.

The PK, 31st in the league a year ago, had twice let the Islanders down earlier in the game. Just 3:23 into the night, Evgeni Malkin tapped one in at five-on-four after Sorokin failed to freeze the puck around the crease. Then, 8:58 into the second, Sidney Crosby boxed out Ryan Pulock around the crease to convert Malkin’s feed across the blue paint at four-on-three.

That accounted for two of Pittsburgh’s three goals through the first 40 minutes, the other one coming from Harrison Brunicke on the rush. Kyle Palmieri scored the Islanders’ second goal, with Mat Barzal — back at center — feeding him 4:04 into the second.

The power play, another point of emphasis all preseason, came up empty too, going 0-for-3, though the Islanders did at least generate chances at five-on-four in a way that was all too rare last season.

But for all the change that came this offseason, and for all the change that was evident on the ice in Pittsburgh Thursday, the Islanders were left ruing the same what-ifs that sunk them a year ago: penalty kill, power play, late-game woes.

They don’t need anyone to tell them that needs to be fixed. They’ve heard it plenty over the years.

Until they do it, though, it will keep hanging over their heads.