Tuukka Rask #40 of the Boston Bruins defends the net...

Tuukka Rask #40 of the Boston Bruins defends the net in overtime against Mathew Barzal #13 of the Islanders in Game 3 of the Second Round of the 2021 Stanley Cup Playoffs at Nassau Coliseum on Thursday, June 3, 2021. Credit: Jim McIsaac

The Islanders have little remaining margin for error, and not only because they trail the Bruins, 2-1, in the teams’ second-round playoff series.

Another reason is in goal, where after benefiting from a shaky opponent in the Penguins’ Tristan Jarry in the first round, they have upgraded to the goaltender big leagues in Boston veteran Tuukka Rask.

That was evident on Thursday night in their 2-1 overtime loss to the Bruins at raucous Nassau Coliseum, where the Islanders’ Semyon Varlamov sandwiched a shaky start and shaky finish with brilliant work in between.

But it was not enough because of an even cleaner outing by Rask, who came within 5 ½ minutes of shutting out the Islanders, then made a big save in overtime shortly before Brad Marchand’s game-winner at 3:36.

So, yes, the Islanders did rally from a 2-1 series deficit against the Penguins to win three in a row, but to reiterate: Tristan

Jarry has left the building.

Mathew Barzal, who tied it with 5:26 left in regulation time, was stopped by Rask at 2:08 of overtime when he tried to put the puck between the goalie’s pads off the rebound of a Jordan Eberle shot. "He was big for them all night, as was Varly," Barzal said. "It’s unfortunate."

That it was, especially when Marchand scored from an extremely sharp angle over Varlamov’s left shoulder.

Rask said he was still recovering from his work at the other end and didn’t see it go in. Neither did Varlamov.

"That’s a seeing-eye puck that he’s got almost a one-inch hole with the puck," coach Barry Trotz said. "That’s a shot that he’ll want back, but he’ll let it go, no different than he’s done many, many times before."

Varlamov said he would have to watch the replay to figure out what happened. "I don’t really have an answer for you right now," he said. "It was kind of a weird shot, but the puck found the net, so it was a good play, I guess, by Marchand."

Varlamov gave up his fourth early goal in four playoff games, this time by Craig Smith at 5:52 of the first period, but after that he settled down and several times heard his name chanted by the crowd of 12,000.

He was particularly good in the third period, during which the Bruins were outshooting the Isles, 19-4, when Barzal tied it. Barzal initially was stopped by Rask’s right pad, then put the rebound past him for his first goal of the playoffs.

That set up a wild final five minutes, including Rask’s stop of Anthony Beauvillier’s second breakaway of the night.

Then came Rask’s stop on Barzal in overtime.

"Tuukka made a great save," Barzal said. "I thought I was in tight and just wanted to sneak one in five-hole."

Trotz acknowledged the Islanders must make things more difficult in front of Rask. "Trust me, yes, you have to," the coach said. "It’s playoff hockey. We’re going to have to get in the interior. We’re going to have to get a little greasy, a little harder on him. He was good; so was Varly."

It has been a strange playoff for Varlamov, who arguably was the Isles’ MVP this regular season, then missed Game 1 against the Penguins because of an injury, then lost Games 2 and 3 and was replaced by Ilya Sorokin.

Trotz reinstated Varlamov for Game 2 against the Bruins even though at the time Sorokin was 4-1 in the playoffs and Varlamov was 0-2. Now he is 1-3.

"I think I was able to deal with the pressure pretty good today and came out pretty strong," Varlamov said.

During his time watching Sorokin, he said he sought extra practice time and tried to stay prepared. "The playoffs is a long run," he said, "so you never know what’s going to happen. So you always have to be ready. That’s what I tried to do."

He did it well. Rask did it better.