The Islanders built a two-goal lead and saw it disappear early in the third period for the second straight night. There was a push back, but they played with fire once too often this weekend.

Claude Giroux scored with 1:40 left in overtime Sunday night at Barclays Center to give the Flyers a 3-2 win over the Isles, who led 2-0 late in the second period behind nothing more than Thomas Greiss and some opportunistic scoring. When Flyers defenseman Ivan Provorov banked a pass off Adam Pelech’s skate and behind Greiss 1:47 into the third to tie the score, it felt just.

“The first two periods weren’t great,” said John Tava res, who pumped 10 shots on goal but could not beat Steve Mason. “Our execution wasn’t as good as the past few games.”

It was Tavares who was stopped on a breakaway in overtime and later gave the puck away to lead to Giroux’s winner. He also spearheaded a power play midway through the third period that came awfully close to restoring the Isles’ lead, with the best chance coming when Ryan Strome snapped one at a yawning net with Mason down and out. Defenseman Radko Gudas saved that shot.

Greiss seemed ready to steal two more points for the Islanders, who came in having won three straight and with Greiss coming off back-to-back shutouts Monday and Thursday. He stopped 33 of 34 shots through two periods, beaten only by Wayne Simmonds after a lazy breakout attempt left Greiss at the mercy of two Flyers within 10 feet.

That goal snapped Greiss’ shutout streak at 154:10 and gave the frustrated Flyers some life. Greiss made 44 saves.

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“We’ve got to figure out our starts,” Doug Weight said, also referring to the slow start to Saturday’s game against the Kings. “It’s a bit of a broken record. We weren’t in cement, but we were in contain mode. When we get on the forecheck, we have to get in there and get down to business.”

Tavares started the play that Nick Leddy finished to open the scoring at 13:25 of the first and Alan Quine chipped a rebound over Mason at 4:47 of the second for a 2-0 lead. That one came soon after the Islanders managed to kill off a five-on-three Flyers power play.

The puck did cross the line just as that two-man advantage expired, but referee Frederick L’Ecuyer ruled that he intended to blow his whistle during a mad goalmouth scramble, so there was no video review.

“We still managed to get that lead, which is a good step,” Quine said. “We certainly had enough chances in the third to win it, too. We showed we can get points when we’re not at our best, and we’ve got to take that positive.”

After a draining week, with Jack Capuano’s firing followed by three games in four nights, perhaps a little fatigue isn’t a surprise. But with the Islanders sitting five points out of a playoff spot and the Blue Jackets and Canadiens coming to Bar c lays Center this week, there’s no time to catch their breath.

“We’ve been playing some good hockey, and that requires energy,” Weight said. “They’ll get their rest, but we’ve arguably had more days off than most. We’ve got a big schedule coming.”