Mathew Barzal slipped behind the defense, swooped in front of the net and beat Braden Holtby with a backhand that put the 2018 Stanley Cup champions on the brink of another early exit.

Barzal scored 4:28 into overtime shortly after Semyon Varlamov made two saves on a breakaway, lifting the New York Islanders to a 2-1 win over the Washington Capitals on Sunday and a 3-0 advantage in their Eastern Conference first-round series.

“Mat wants to be that difference-maker and he got an opportunity and he capitalized," New York coach Barry Trotz said.

The sixth-seeded Islanders have put Washington within a loss of being eliminated in the first round for the second straight year after hoisting the Cup.

“Obviously, for us right now it’s nothing to lose, right? So we just have to go out there and play," Washington star Alex Ovechkin said. “Don’t think about the score in the series."

Holtby had 32 saves for the third-seeded Capitals, who have to win Game 4 on Tuesday night to extend the best-of-seven series.

“I know it’s a hard situation, but it’s not over yet,” said Ovechkin, who had one assist and one shot Sunday. “We won the Cup when we were down 2-0 against Columbus, coming back, and we’re going to try.”

New York’s Anders Lee broke a scoreless tie late in the first period. Evgeny Kuznetsov pulled the Capitals into a tie with a power-play goal early in the second.

Varlamov stopped 22 shots, including two in overtime when Jakub Vrana had a breakaway shortly before Barzal scored the winner off Jordan Eberle's pass that took advantage of poor defensive positioning.

“I just should have been sagged off a little bit more to give myself a better chance at the puck," Capitals defenseman John Carlson said.

The 23-year-old Barzal was thankful the play wasn't called offside.

“We knew it was tight," he acknowledged. “I run that play a little bit in practice and even in games, try to sneak behind the D, and time it perfectly on the blue line. Great heads-up play by Ebs, great touch on the pass."

For the first score, Lee skated into an opening on the right side of the net and tapped his stick to get the puck. Adam Pelech perfectly placed a diagonal pass on Lee's stick and he pushed it in to put New York ahead 1-0 with 5:10 left in the opening period.

“He put himself in a great spot — just had to get it to him," Pelech said.

Kuznetsov scored on a power play 5:50 into the second period on a wrist shot from the top of the right circle.

New York finished 0 for 5 on the power play while Washington was 1 of 2 with an extra skater.

The Capitals appeared to start the game sluggish and were fortunate Holtby bounced back with a solid performance after giving up four goals in each of the first two games.

Washington coach Todd Reirden will have to figure out how to help his team generate more scoring to stave off elimination perhaps without Nicklas Backstrom, who missed a second straight game in concussion protocol.

When Trotz resigned two years ago, the Capitals promoted his top assistant, Reirden, to take over from the bench. And now, Reirden's job is to try to outcoach his old boss.

“I put pressure on myself all the time," Reirden said. “I have belief in myself as a coach and belief in our team and our leadership group that we can focus on getting this one win here and seeing where that takes us from there."

NOTES: Lee has scored in all three games in the series against Washington. ... The Capitals scored just two goals in each of the first two games. ... Washington center Brian Pinho played in his first NHL game.