New York Islanders goalie Thomas Greiss (1) makes the save...

New York Islanders goalie Thomas Greiss (1) makes the save during the second period of Game 4 of the Eastern Conference semifinals against the Tampa Bay Lightning on Friday, May 6, 2016 at Barclays Center. Credit: Jim McIsaac

There is almost no distance between the Islanders and Lightning. You could describe it by holding two fingers less than a half-inch apart. That is how close the teams have been. Except the Lightning is way ahead.

That is how the playoffs go, especially in the current version of the parity-driven NHL. The slightest edge, the subtlest break can make all the difference in the world. It helps if you have the poise and experience of having been to the Stanley Cup Final last year. So it is with the Lightning, which has been just good enough at just the proper time to lead the series 3-1 and have the Islanders right on the brink.

As is their custom, they tried not to look backward.

“It’s just how it goes. It’s a long series. You just have to wait for the bounces and they will come,” said Islanders goalie Thomas Greiss, who had to leave briefly during the second period because his skate broke.

Truth is, though, it might be their hearts that were broken. For the second game in a row, the Islanders let a lead slip away in the third period. Quite possibly they let this second-round series slip away as well.

Having led most of the night, the Islanders gave up a goal 7:49 into the final period — Nikita Kucherov found the slightest opening on Greiss, at the same end at which John Tavares’ shot rang off the post a period earlier — then quickly lost it in overtime. Jason Garrison scored on a wild scramble of a play at 1:34 of OT.

It gave the Islanders a sinking feeling of what “sudden death” really means. They are good and disciplined, always looking to the next game. But at some point, they might look back at Game 3, when they lost a lead in the last minute of regulation and fell in overtime. That would have given them some margin for error and maybe a bit of extra confidence against an opponent that seems to have a ton of it.

No such luck, though. It was the Islanders’ misfortune that Calvin de Haan’s stick broke and there was a sudden burst of helter-skelter play in the overtime. “A guy gets a shot, I block it, but he goes D to D,” Johnny Boychuk said, referring to the two Tampa Bay defensemen. “And a one-timer.”

That was all it took. Credit to the Lightning for putting itself in position and never getting discouraged in either of these two games at Barclays Center. Unless they can win in Tampa on Sunday, the Islanders will have a while to think about how they could have put themselves ahead by more than one goal and avoided another sudden nightmare. For a second straight game, they delighted a raucous crowd by outplaying the opponent, but they just couldn’t put the Lightning away.

“It’s a fine line. Obviously, we did a lot of good things tonight,” Tavares said. “We had a lot of opportunities. We just didn’t seem to get the breaks. Cal’s stick broke in overtime there. We’ve just got to find a way to overcome that. It’s not always going to go your way. We’ve just got to stick with it, trust our game and try to build off the good things. We didn’t give them a whole lot.”

There are no laughers or breathers in these playoffs. Including the Islanders-Lightning Game 4 on Friday night, 41 of the 63 games in this postseason entered the third period either tied or with a one-goal difference. It sure makes every shift, every shot, every save, every block extra intense.

“When you eliminate 14 teams and you’re down to 16 and you eliminate eight more and you’re down to eight, it’s razor-thin, the margin of winning and losing,” Lightning coach Jon Cooper said before the game, holding his thumb and forefinger less than a half-inch apart.

Sometimes. though, that little bit of a difference can seem like miles.