Jaroslav Halak was back in net, but it didn't matter. A three-goal lead in the third period is simply not secure these days for the Islanders.

For the second straight game, they let what seemed like a sure victory turn into a far more tenuous situation.

If not for Johnny Boychuk's power-play goal in overtime, the Islanders might have left Nassau Coliseum feeling far worse than they already did Monday night.

But Boychuk's slap shot with four seconds remaining on the power play and 2:08 left in the extra period gave the Islanders a far-too-difficult 4-3 win over the Washington Capitals.

"There are always ups and downs in the season," John Tavares said. "Sometimes things don't go your way, and it's all about how you respond. We found a way."

Calvin de Haan scored a shorthanded goal 1:41 into the third period to give the Islanders a seemingly comfortable 3-0 lead with their starting goalie back in net for the first time in a week. But much like Saturday night in Buffalo, the three-goal lead dissipated quickly.

The Sabres scored three times in the third period of that game to force overtime and won in a shootout. On this night, the Capitals responded with two goals in the span of 1:49 and Alex Ovechkin tied it at 3 with 2:41 left, firing a shot past Halak without anybody in between them.

The sellout crowd at Nassau Coliseum that had been so boisterous at the start of the period suddenly was silent. Boychuk said he could hear fans yelling "shoot!" when he had the puck in overtime.

It's the fourth time this season the Islanders have blown a three-goal lead, but coach Jack Capuano did his best to brush it aside. He said he was pleased with how the Isles played in the final period Monday night, much as he insisted he was pleased with their performance in Buffalo.

"If we were playing poorly, it would be one thing," he said. "I've been here when we've been playing poorly and teams have come back."

Halak returned after missing two games because of a lower-body injury, and before the Capitals' comeback, he had showed very little rust.

But Washington's Eric Fehr beat him to make it 3-1 at 4:40 of the third period. Then Nicklas Backstrom broke free from the pack for a clear look at Halak and brought the Capitals within 3-2.

Until then, things were going well for the Islanders.

Anders Lee opened the scoring midway through the first period with some nifty stickwork. With his back to the net, he broke free from former Islander Jack Hillen in time to deflect a hard shot from Ryan Strome past goalie Braden Holtby, all without his eyes on the net.

The Islanders made it 2-0 with a power-play goal credited to defenseman Lubomir Visnovsky at the 10:06 mark of the second period.

Notes & quotes: Capuano expects Michael Grabner to return Wednesday when the Islanders begin a seven-game, two-week road trip in Winnipeg. Grabner, who was on the ice during Monday's optional skate, has played in five games and none since Dec. 13.