Mark Herrmann Newsday columnist Mark Herrmann

Herrmann has covered the Mets and Yankees since 1988, and has been Newsday’s national golf writer since 2002.

This is how it works sometimes in playoff hockey, at least in the frustrating world of Islanders playoff hockey: A big question mark turns out to be the one rock of strength. Anyone who wondered if Thomas Greiss could get up to speed in the postseason ought to wonder if the rest of the team can catch up to him.

A goalie who never had started in the NHL playoffs before last week was the best Islander on the ice from start to finish last night in Game 4, which became another lost opportunity. True, he did allow the winning goal by an unlikely source, defenseman Alex Petrovic, at 9:25 of the third period. But it would not have been a 2-1 nail-biter had Greiss not kept them in it during a lackluster first period.

Jack Capuano admitted that the first 20 minutes of the loss to the Panthers were perhaps the worst the Islanders have played all year, and you have to ask yourself how that can happen. The team had support from a frenzied crowd at Barclays Center. It had all the motivation, too, with a chance to take win successive playoff games for the first time since 2002 and move closer to winning a series for the first time since 1993.

Still, at the start of the game, there was not much there, other than the man who had been signed to be a backup goalie and has wound up being The Man after starting goalie Jaroslav Halak went down with an injury.

“I think we’re confident. We didn’t play a bad game today,” Greiss said after having made 27 saves and been named No. 2 star of the game [Petrovic was No. 1]. “We just need a little energy and push back . . . I think we just have to be more aggressive, play more in their end, it makes life easier on our defensive end.”

Greiss withstood Jonathan Huberdeau barreling in on a breakaway in the second period, crashing into his pads and knocking the puck into the net. The goal was disallowed. He allowed a power-play goal, as did his Panthers counterpart, Roberto Luongo. Of the winning shot, with 10:35 left, Greiss said: “A couple of guys went down in front of me. I picked it up late.”

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It happens. When you are a goalie, you play on because you have to be ready for anything. Goaltending remains an open question in this series, what with Luongo being 37 and 17 years removed from a stellar 43-save career debut for the Islanders. But if Greiss can play two or three more games like he did Wednesday night, it should be enough for his team to win.

He sounded calm afterward, embracing the challenge rather than regretting a lost opportunity. “I enjoy playing hockey, I do my best,” he said. “That’s all I can control. That’s all I worry about.”

Greiss made huge saves this season even when the Islanders weren’t playing. After the Jan. 23 blizzard and the postponement of a game against the Flyers, he went with his wife to Home Depot, bought a tow rope and freed many Long Island motorists from hopeless snow banks. So he is a good soul.

But he has grit, too. Capuano likes his goalie’s competitiveness and fitness, saying the latter is the best he has seen in a goaltender. These are not the old days, when Al Arbour reportedly ordered Billy Smith to ride the stationary bike in the locker room and Smith predictably bristled, saying, “Hey Al, what do you want, a goaltender or somebody who can win the Tour de France?”

In those days, though, the goalie’s intensity was matched by firepower up front. The Islanders who took the ice in a raucous arena Wednesday night couldn’t match the fire in the fans’ voices or the goalie’s heart. After this game, there were many new questions to answer.