Another blown lead. Another home loss. Another scoreless night on the power play. Another chance the Islanders let slip through their fingers.

Play it again, Sam.

The Islanders left the UBS Arena ice on Wednesday night to the same soundtrack of disappointment that has become commonplace since they returned from Western Canada more than a week ago. For the fourth straight game, they scored first. For the third of those four — and fourth of five at home — they lost. And after falling 4-1 to the Bruins, the Islanders (23-19-4) have now lost this season as many times as they have won.

“Is it a low point? Again, we need to collect some wins here,” coach Lane Lambert said. “It’s a tough league, it’s an unforgiving league and no one is feeling sorry for us.”

Their points percentage is still above .500, and the league-leading Bruins were always going to be a tough team to earn two points against. But at the end of the day, the Islanders wasted a great first period and lost a game they could have won.

“Right now it’s the little things, our mistakes seem to be the ones that end up in the back of the net,” captain Anders Lee told The Post. “We’re not giving ourselves the cushion to have those, and so in tight games when you play solid but you make a couple errors here and there, they cost you.”

The Islanders hung tight with the Bruins, even after a 1-0 lead turned to a 2-1 deficit, but it’s hard for a team to win against such ruthless opposition when its power play is riding a goal-scoring drought and its goaltender is anything but perfect.

Semyon Varlamov, who stopped 21 of 25 shots for the Islanders, looked rusty playing just his second game in a month, and his team looked better at even strength than at five-on-four, wasting five power play chances.

“The power play didn’t help us at all tonight,” Lee said.

“Killed us tonight,” Mathew Barzal said. “It’s lost us some games recently.”

The Bruins salted the game away on their own power play, as Brad Marchand slapped home a feed from David Pastrnak that went untouched through the slot at 5:03 of the third period. That made it 3-1, and though there were nearly 15 minutes left in regulation, the Islanders are not a team that currently seems capable of turning around a two-goal deficit.

The Islanders got their fifth chance on the power play just 33 seconds after Marchand’s goal. After Zach Parise’s redirect from the doorstep caromed off the post — a symptom of a snakebitten unit if there ever was one — they had made it a clean three for their last 50 tries at five-on-four.

To pour salt on the wound, Trent Frederic directed Charlie Coyle’s feed straight into the roof of the net with 4:22 to go in the game, making it 4-1. As Islanders fans made for the exits, a “Let’s Go Bruins” chant took hold at UBS Arena, and the road team left the ice to a standing ovation.

The Bruins started digging their heels in during the second period, when Charlie McAvoy tied the score with a one-timer off Matt Grzelcyk’s feed at 7:48. A little more than four minutes later, Derek Forbort poked in a rebound that Varlamov left in the crease to hand the lead to Boston. After turnovers by William Dufour, who was making his NHL debut, led to both goals, he was nailed to the bench for the rest of the night, and played just 6:48 total.

Barzal was asked in the locker room whether the season is slipping away from the Islanders, who are now a point behind Pittsburgh for the last wild-card spot in the Eastern Conference with two fewer games played.

“Absolutely not,” he said.

It’s true that the Islanders are far from out of it. But something needs to change. Fast. And preferably on the power play.

“The results right now don’t sit well with anyone in this room,” Lee said of the three-for-50 skid. “We’re gonna do whatever we can to make sure it’s better.”