The 5-1 defeat of the Toronto Maple Leafs at Verizon Center also made sure the Canadian side would not be figuring in the post-season.
Alex Ovechkin, Martin Erat, Jack Hillen, Troy Brouwer and Marcus Johansson were on target for the Capitals, with Mikhail Grabovski breaking the home shut-out in the final period.
The New York Islanders are also closing in on a place in the play-offs, with a 5-2 win over the Florida Panthers strengthening their case.
Michael Grabner (two), Mark Streit, Matt Moulson and Radek Martinek got the victors' goals at Nassau Veterans Memorial Coliseum, with Dmitry Kulikov and Marcel Goc replying.
The Ottawa Senators improved their own play-off prospects with a 3-2 win over the Carolina Hurricanes at Scotiabank Place, while the Philadelphia Flyers did likewise in seeing off the New York Rangers 4-2.
Kyle Brodziak scored twice as the Minnesota Wild dealt another blow to the Edmonton Oilers' slim hopes of playing a part in the end-of-season extravaganza. Charlie Coyle, Mikael Granlund and Zach Parise also scored in a 5-3 success, with Nail Yakupov, Magnus Paajarvi and Shawn Horcoff replying.
Andrew Ladd netted twice in regulation and added the decisive goal in a shoot-out as the Winnipeg Jets kept their play-off hopes alive with a 4-3 victory over the Tampa Bay Lightning.
Alexander Steen's shoot-out goal gave the St Louis Blues victory over the Vancouver Canucks, who led through Alexander Edler's first period goal but were pegged back by Jay Bouwmeester's marker.
In the day's late game, San Jose established a 2-0 lead against the Los Angeles Kings but were taken to a shoot-out - during which Raffi Torres held his nerve to give the Sharks the win.
Meanwhile, the Ottawa Senators' match at the Boston Bruins - postponed on Monday after the Boston Marathon bombings - has been rescheduled for April 28 at TD Garden.