Ladd put the Islanders back in front late in the second period, but Ovechkin made it 2-2 at 1:17 of the third with his 16th goal of the season. Halak made an initial save on Williams' shot from the left circle, but Ovechkin was on the doorstep for the rebound.
Ladd scored his second goal of the game when he redirected Quine's feed past Holtby at 4:41, and Lee made it 4-2 when he scored on a breakaway 43 seconds later.
"Once you're a scorer, you're a scorer," Islanders coach Jack Capuano said of Ladd. "They're gonna come. Even last year, it came in bunches for him after Christmas. He works hard. If you continue to work hard, good things are gonna happen. He went to the net twice, that's where the goals were."
Burakovsky got the Capitals back within one with 6:55 remaining, his second goal in the past three games.
Washington had two power plays in the final 5:15 but failed to score.
"I don't think it should've gotten to that point, to be honest," Williams said. "I don't think we played well. I don't think we forechecked well. I don't think we talked well. Maybe that was because of the [Christmas] break. Whatever it was, we certainly just weren't sharp tonight. Not sharp enough to win."