Daniel Sprong extended it to 4-0 when he scored on a breakaway at 15:07.
"Obviously, a solid shot," Ovechkin said of Sprong, who has scored a goal in three of the past four games. "I always tell him, 'Just shoot the puck and you never know what's going to happen.' I think right now he's on a hot streak and he looks good, and it's good for us."
Garnet Hathaway tipped in defenseman Justin Schultz's shot from the point to make it 5-0 at 6:46 of the third period.
"I think that's been a big problem for us, is burying our offensive opportunities," Okposo said. "I've never seen it through 27 games like the way it's gone with essentially everybody. It's just unfortunate. It's tough, it's tough right now."
NOTES: Ovechkin is 14 goals behind Marcel Dionne for fifth in NHL history (731). … Schultz, forward Conor Sheary and defenseman Nick Jensen each had two assists for the Capitals. … Kuznetsov's goal was his 400th NHL point. … Backstrom played his 984th NHL game, passing Calle Johansson for second in Washington history behind Ovechkin's 1,176. … The Sabres, who lost 3-0 to the Pittsburgh Penguins on Saturday, have been shut out in consecutive games twice in their past 10 after also losing 3-0 to the Philadelphia Flyers in back-to-back games Feb. 27 and 28. … Buffalo has not won since Feb. 23 (4-1 at the New Jersey Devils) and has been outscored 46-17 in the 11 consecutive losses.