DALLAS — There wasn’t much that needed to be said after two periods Thursday night. The Islanders had some strong moments but too many “stupid plays,” as Doug Weight referred to them, that had them trailing the Stars by a goal entering the third.

“We had to play a simpler game — hold on to pucks, get someone in front, be smarter,” Dennis Seidenberg said. “It wasn’t a big mystery.”

The Islanders solved that puzzle with three goals in the first half of a dominating third period that propelled them to a much-needed 5-4 win. It was the Isles’ second win in the 20 games in which they’ve trailed after two periods (2-16-2).

Seidenberg snapped a 3-3 tie at 7:46 with a wrist shot through Jason Chimera’s screen after a fortunate-bounce goal by Nick Leddy and before Leddy set up Nikolay Kulemin for a two-goal lead.

They had a 10-0 shot edge as they turned a 3-2 deficit into a 5-3 lead, not allowing the Stars to do anything in their zone. Weight chided his team for making a few more “just really stupid mistakes” that allowed Jamie Benn to score shorthanded with 2:51 to go to cut the Isles’ lead to one, but Thomas Greiss made three of his 21 saves in the final minute to preserve the win.

The key in the third was getting contributions from defensemen. Leddy’s tying goal 25 seconds into the third proved to be a nice accident. Antti Niemi stopped Leddy’s shot, but the puck caromed hard off the end boards, off the back of Niemi’s leg and over the line.

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Calvin de Haan made a strong pinch to get the puck to the slot before Seidenberg whizzed home his first goal in 44 games to give the Isles the lead. Leddy’s speed rush left three Stars in the dust before he wheeled it to Kulemin for a goal at 9:29 that made it 5-3.

“Even at the end of the second, we got one back and we were buzzing,” Weight said. “Our D were active, they were up in the play and our forwards did a good job along the walls to find them. We’ve been missing that for a few games.”

Weight couldn’t let the first two periods slide in his postgame comments, nor did his players let them drop, either.

The Islanders had the greater share of the scoring chances through 40 minutes, but the Stars’ chances were high quality. Greiss was left flailing on Benn’s first goal with 7.4 seconds to go in the first period, which tied it at 1-1, and on second-period goals by Radek Faksa and Jason Spezza, both of whom were left untouched to Greiss’ right before snapping shots past him.

“It’s encouraging the way we played in the third, but it’s also dangerous,” Seidenberg said. “You don’t want to rely on one period to save you. We can control the game if we’re smarter with the puck. We can’t dig ourselves a hole.”

Josh Ho-Sang had a strong night in his NHL debut, nearly scoring on a couple of chances.

Ryan Strome had the Isles’ first goal and added two assists. Despite allowing four goals, Greiss was strong enough for Weight to consider using him again Friday night in Chicago.

And it was a huge two points to keep pace with the teams around the Islanders in the chase for the final Eastern Conference playoff spot. The Islanders are tied with Toronto for the second wild card and have a game in hand on the Maple Leafs.

“You don’t want to keep looking at the standings that much,” Leddy said, “but it was [a must win]. We played great in the third, and that’s what we needed.”