The Capitals were made to work for everything they got, eventually eking out a 3-1 victory at the Scotiabank Saddledome.
"In the third, we had a pretty good push but it wasn't good enough," said Mikael Backlund. "We've got to find a way to play way better at home and have better starts.
"It's our barn and have to show teams that when they come here it's not going to be an easy game.
"We've got to show them right away it's going to be a tough, long night for them."
Largely second best for a long stretch, the Flames made a determined push in the third against a Capitals' crew that had played, and won, Saturday night out on the west coast against the Vancouver Canucks.
After generating only 14 shots through 40 minutes, the Flames rallied, testing Washington goaltender Braden Holtby on numerous occasions.
Their best chances fell to ex-Cap Troy Brouwer early in the period and Backlund, whose high backhander through a tangle of bodies was blocked and held by Holtby on his chest.
But it was not to be, Marcus Johansson finding an empty Flames net for the clincher in the game's final minute.
"It wasn't the start we were looking for and I thought we were not as dialed in as we needed to be," Flames coach Glen Gulutzan said. "We did a couple things wrong and usually when you do a couple things wrong, something bad happens.
"We played a really good hockey club, I think they're real solid … they had a lead and they played with it for nearly sixty minutes."