Nicolas Roy had a goal and two assists, Alec Martinez had a goal and an assist, and Logan Thompson made 20 saves for the Golden Knights (29-16-2), who had lost three straight and finished their seven-game homestand 3-4-0.
"I think this win goes a long way for everyone. It's a big confidence boost," Thompson said. "Scoring's been tough for us of late, and keeping the puck out for the goalies has been tough as well, so I think every position can build off this."
T.J. Oshie and Marcus Johansson scored for the Capitals (25-18-6), who had won nine of their past 10 road games. Darcy Kuemper allowed four goals on 18 shots before being replaced in the second period by Charlie Lindgren, who made seven saves.
"I'm not going to get too much into it," Washington coach Peter Laviolette said. "We weren't good. They were the better team, and we'll get ready for the next one. There are things that we can go back and try to get better at."
The Capitals played without captain Alex Ovechkin, who did not take part in the morning skate and is day to day with a lower-body injury. Laviolette said was unsure whether Ovechkin would be able to return against the Colorado Avalanche on Tuesday.
"There's always things that are going on with players," Laviolette said of Ovechkin's injury. "Alex is usually really durable, but this is something that he wasn't able to skate this morning and it took him out of the lineup tonight."