There was a stretch of the second period on Tuesday when the Islanders showed some life, sparked by 19-year-old Anthony Beauvillier’s first NHL goal.

But that stretch was dwarfed by far longer durations of inconsistent play and the Islanders being a step behind the Sharks. That was the case on Joe Pavelski’s game-winner with 2:11 to play, a redirection from the high slot where Pavelski got his stick down in free space right in front of Nick Leddy to send the puck over Jaroslav Halak’s shoulder and give San Jose a 3-2 win at Barclays Center.

“We could’ve defended that play a little harder,” Jack Capuano said after his team fell to 1-3-0 on the season. “We’ve got pretty good position there, but you’ve got to get sticks (tied up).”

That wasn’t the only failing for the Islanders in facing Sharks rookie goaltender Aaron Dell, who was making his NHL debut. The Isles mustered only four shots on Dell in the opening period, none after the five-minute mark had elapsed. The Isles, who out-attempted the Ducks 27-5 in the first period on Sunday, had only nine attempts at the net in Tuesday’s first period.

They left the ice after one trailing by a goal on Melker Karlsson’s score from the top of Halak’s crease.

Asked if the slow start was more San Jose than the Islanders, Travis Hamonic shrugged. “Probably us,” he said. “You can’t (compliment) them for us not having our legs at the start. It felt like we were a step slow.”

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That extended into the middle of the second, with the Sharks coming off a 7-4 loss to the Rangers on Monday clearly looking to play a simple, physical road game and keep Dell’s crease clean.

In stepped Beauvillier, the young forward playing his third NHL game. He jumped off the bench and onto a feed from Josh Bailey, throwing a backhand towards the net that was blocked. Beauvillier followed and shoveled another try that flipped up on Dell and the goaltender waved the fluttering puck into his own net at 9:39 of the second.

“I was pretty happy, pretty excited,” Beauvillier said. “I was on the bench smiling, so I was pretty excited for sure.”

The Isles jumped ahead 2:10 later when Anders Lee snapped a nifty saucer pass from Jason Chimera past Dell and the building and the home bench had some life. The Isles pressed for a two-goal edge, with Cal Clutterbuck ringing a shot off the post, before the Sharks pulled even off another Isles lapse.

Controlling play, the Islanders retrieved a puck and iced it with just over two minutes to go in the second. Joe Thornton beat Casey Cizikas on the faceoff, the puck worked around the Isles zone and Thornton threw a puck to the crease, where it banked off Tomas Hertl’s leg and behind Halak at 18:03.

“I haven’t coached a team in a lot of years that gives up this many goals after we ice the puck,” Capuano said. “We’re dominating a shift, we ice it and it’s in the back of our net. They just threw the puck from the side.”

Capuano was disappointed his team managed only 23 shots on Dell and were out-attempted 54-44. Pavelski took a delay of game penalty with 1:06 left, giving the Islanders a six-on-four advantage with Halak pulled, but they didn’t get off a shot inside the Sharks zone with that edge.

“We were too slow at times and it cost us,” Lee said. “Just playing catch-up all night. They were coming in off a back-to-back and they played smart. We just didn’t.”