The Islanders, playing their first game without suspended forward Chris Simon, rebounded from a pair of 2-1 losses to the rival New York Rangers and sent the Capitals to their fifth regulation loss in seven games (0-5-2).
Mike Sillinger and Jason Blake also scored for the Islanders, who moved three points ahead of Carolina and the playoff cutoff in the Eastern Conference. Rick DiPietro stopped 26 shots to reach 30 wins for the second straight season. He made his 17th consecutive start and played in his 200th NHL game.
Blake sealed it with his career-best 35th goal, scoring into an empty net for the Islanders, who have earned points in 19 of 22 games (13-3-6).
Alex Ovechkin and Donald Brashear scored 1:49 apart in the third period, but it wasn't enough for the Capitals. Washington, beaten 3-0 by Toronto and Carolina in its previous two games, avoided the franchise's first three-game shutout streak and snapped a goal-less drought of 176 minutes, 14 seconds.
Simon was suspended indefinitely by the NHL on Friday after his two-handed stick attack against Rangers forward Ryan Hollweg on Thursday and served the first game of his banishment just hours after attending a disciplinary hearing in New York.
In a statement released during the game, Simon apologized for his actions and said he was diagnosed with a concussion as a result of a check from Hollweg that led to his harsh retaliation.
The Islanders scored twice against Capitals goalie Brent Johnson in the first period and built a 4-0 lead through 40 minutes.
Sillinger got things going two minutes after the opening faceoff when he let go New York's first shot of the game from the top of the right circle - during a 2-on-1 with Hilbert - and fired it past Johnson for his 23rd of the season and second against Washington in a week.
Hilbert scored with 7:19 left in the period, sending a drop pass from Bergeron off the right post, off Johnson and in. It was Hilbert's first goal since Jan. 27 against Buffalo.
The surge continued in the second period, the frame in which Johnson shined on Friday against Carolina but couldn't duplicate. Johnson, making his 11th start in 12 games since regular goalie Olie Kolzig went down with a knee injury, stopped 40 of 42 shots - including 20 in the second period - in the loss to Carolina.
Blake gave New York a 3-0 lead at 12:30. Bergeron then scored his 11th of the season, eighth on the power play, with 1:28 left in the period.
Ovechkin finally got the Caps out of their scoring drought 4:27 into the third, following up his own rebound to make it 4-1. He was less than a period away from matching his longest point skid of the season, having gone three straight games without a goal or assist. He went pointless in eight of the previous 11 games.
Brashear recorded a goal and a knockout in a matter of seconds. The brawny forward smacked a rebound past DiPietro at 6:16 for his first goal in 17 games. Former Caps defenceman Brendan Witt came toward him, drawing a shove from Brashear. Witt moved closer and took a left to the jaw from Brashear that flattened Witt on his stomach.
Notes: Steve Eminger returned to the Washington lineup after a one-game absence, taking the place of former Islanders D John Erskine, who will miss the rest of the season after dislocating his thumb Friday. ... New York C Viktor Kozlov missed his first game of the season, sitting out with a sore foot. The Islanders recalled Jeff Tambellini from AHL Bridgeport. ... Islanders RW Miroslav Satan played in his 300th straight NHL game.