Reimer allowed four goals on 13 shots and was pulled in the first period of the Sharks' previous game, a 7-1 loss to the Tampa Bay Lightning on Saturday.
"Any time things don't go your way, you want to come back and play well or do what you can," Reimer said. "Obviously, you never know what's going to happen out there, but you want to try and bring your A game and let the chips fall where they fall."
Nicolas Meloche scored his first NHL goal for the Sharks (22-19-2), who had lost four of five (1-3-1) and were starting a four-game road trip.
"I don't know if I'd say it's the biggest [win] of the year, but it was definitely a response game," San Jose coach Bob Boughner said. "That's what we stressed the last couple days: showing up, responding and picking ourselves up off the floor."
Daniel Sprong scored for the Capitals (23-12-9), who have lost consecutive games in regulation for the first time this season and are 3-6-2 in January. Ilya Samsonov made 26 saves.