Washington earned the game's first power play on the game's first shift, but it was the Sens who jumped out to an early lead while Dion Phaneuf was in the box for slashing Alex Ovechkin.
Ottawa defenseman Fredrik Claesson picked off a Marcus Johansson pass near the right circle of the Sens' zone and left the puck for Tom Pyatt, who skated it out of the zone and fed Chris Kelly. Pyatt and Kelly exchanged the puck a couple of times as they skated up ice with speed, and Pyatt finally went back to Kelly, who chipped a backhander past Caps goalie Philipp Grubauer for a 1-0 Ottawa lead at 1:46 of the first, on the Senators' first shot on net of the game.
An Ovechkin hi-sticking minor cut short the remainder of the Washington power play, giving the Sens an abbreviated man advantage.
Seconds after the Caps killed that penalty, Grubauer made a great stop on Bobby Ryan from point blank range. But Derrick Brassard collected the rebound and went to Claesson with it. The Ottawa blueliner fired from center point, and Ryan tipped it past Grubauer at 4:10. With that Ryan goal the Sens doubled their lead, and doubled the number of goals they had scored in the first two meetings between the two teams this season.
Grubauer did his part to keep the Caps close all night, making a huge save on Ryan Dzingel early in the second period. When Washington's torrid power play got a chance to go to work a few minutes later, the Caps had a chance to halve the Sens' lead. But Ottawa's penalty killers stiffened and kept Washington at bay.
Near the middle of the second, the Caps got sloppy with their sticks, taking a pair of unnecessary stick fouls within a short span of time. Washington killed the first of those calls, but Ottawa's Zack Smith made it a 3-0 game with a redirection of Dzingel's shot, and that power-play goal sent the Caps to their largest deficit at any point in nearly two months.
Washington had four more extra-man opportunities thereafter, but was unable to catch a spark or to get anything started offensively. In Monday night's 6-1 win over the Carolina Hurricanes, the Caps were able to consistently establish a net presence and to put pressure on the Canes down low in the attack zone. They had no such success on Tuesday in Ottawa; the Sens were effective at walling off the interior, and on the occasions when Condon put a rebound in a dangerous area, his teammates were always easily the first ones to get to it.