The Caps doubled that advantage on a power play in the back half of the first frame. Alex Ovechkin took a shot from the left side, and Calgary goalie Mike Smith made the stop. But T.J. Oshie was first to get to the rebound, and he roofed a backhander from the top of the paint to make it 2-0 at 14:27.
That two-goal cushion was short-lived. Calgary got on the board just 15 seconds after the Oshie goal, cutting the Washington lead in half when Johnny Gaudreau's intended centering feed clanked off the left skate of Flames defender Travis Hamonic and behind Copley at 14:42.
When Brett Connolly was deemed guilty of an interference minor in the offensive zone, Calgary went to its first full power play of the afternoon. Nine seconds later, Elias Lindholm snapped a shot past Copley from right dot, tying the game at 2-2 with 3:06 left in the first.
Late in the second, the Caps regained the lead with a second goal in as many games from their fourth line. Connolly carried the puck out of the right wing corner and left it for Matt Niskanen at the right point. Niskanen floated a shot through traffic and behind Smith to lift the Caps back into the lead, 3-2 at 16:57.
For most of the remainder of regulation, it looked as though Niskanen's goal might stand up as the game-winner. The Caps played road hockey in the third and got pucks deep routinely, but the Flames - still stinging from a 9-1 home ice loss to Pittsburgh on Thursday - brought it all in the third.