With Jacob Markstrom struggling, Dan Vladar made his fourth start in the last six games and was solid in making 27 stops. He improved to 3-4-1.
With the Flames nursing a 2-1 lead late in the third, Ruzicka and Mangiapane put the game out of reach scoring 55 seconds apart.
At 13:39, Ruzicka got behind the Capitals' defence, corralled Backlund's high pass with his glove as he crossed over the blue line, then snapped a shot over Lindgren's glove on a breakaway.
Tied 1-1 after the first, the Flames regained their lead 1:35 into the second when Mangiapane took a pass from Backlund and wired a wrist shot from about 25 feet out over Kuemper's shoulder.
The top corner was also the formula for Calgary's opening goal at 18:03 of the first period. Coleman beat Kuemper far side from a similar distance to that of Mangiapane's marker, after being set up by Ruzicka.
Calgary looked to take its lead into the first intermission, but a roughing penalty late in the period against Dube proved costly. With 34 seconds left, Sheary was left open in front and sent a quick shot past Vladar off a pass from Sonny Milano.
Already missing six players due to injury, Washington lost two more in the second period. Halfway through, defenceman Martin Fehervary was shaken up when he was hit along the corner boards by Milan Lucic. Shortly after, Kuemper pulled himself from the game after a skirmish with Tyler Toffoli.
Calgary continues to struggle on the power play. After going 7-for-23 through its first six games, good for fourth-best in the NHL, an 0-for-3 night against the Capitals has put the Flames at 7-for-54 since, which is third-worst in the league.
ALL-TIME GAMES LISTS
Washington left-winger Alex Ovechkin played in career game No. 1,300. He is the 14th player all-time to reach that number with the same team. He's also one game away from tying Sergei Gonchar (1,301) for second-most career games in the NHL by a Russian. Alex Kovalev (1,316) is the leader.
Capitals: Six-game road trip continues on Monday against the Edmonton Oilers.
Flames: Return to action on Monday when the Arizona Coyotes visit the Saddledome.
This report by The Canadian Press was first published Dec. 3, 2022.
Darren Haynes, The Canadian Press