But Jake Voracek, after taking a slick pass from Scott Hartnell, gave the Flyers a 5-3 lead with 8:09 remaining, scoring from the slot for his second goal of the night and 18th of the season.
The Caps didn't quit. Brooks Laich's tip-in - Washington's third power-play goal of the night - got the Caps within 5-4 with six minutes left. Washington had a season-low eight shots over the first two periods, then had 17 shots in the final period.
Steve Downie's first goal in 27 games - an empty-netter - locked up the win with 51.9 seconds left.
The Flyers jumped out to a lead 6:48 into the game, when Sean Couturier did the dirty work and Giroux supplied two sensational moves on the game's first goal. Couturier checked defenseman Jack Hillen into the boards near the blue line, knocking the puck free for an on-charging Giroux, who swooped around Ovechkin and undressed goalie Braden Holtby with a deke before putting a backhander into an empty net.
"Coots did a real good job of getting the puck," Giroux said.
Just 1:34 later, Voracek, set up nicely by Giroux, scored a power-play goal from the high slot to make it 2-0.
With 8:01 left in the opening period, Flyers defenseman Luke Schenn legally checked Ryan Stoa, but Washington's Tom Wilson took exception. Schenn got the best of Wilson in their heavyweight bout, and then Vinny Lecavalier and John Erskine fought down one end of the ice and several players tried to jump in.
When order was restored, the teams were assessed with a combined 56 penalty minutes, and Erskine and Lecavalier were ejected for getting involved in a secondary fight.
Fittingly, the melee occurred on the 10-year anniversary of a Flyers-Ottawa game that produced an NHL record 419 penalty minutes and 16 - yes, 16 - ejections.
In the second period, Giroux scored his 22d goal, and Adam Hall (tip in of Schenn's blast) added his fifth as the Flyers built a 4-0 lead and sent Holtby (four goals on 18 shots) to the bench. Holtby was relieved by Philipp Grubauer, who was recalled from Hershey earlier in the day and had been scheduled to make an appearance at a Turkey Hill Minit Market in Lancaster on Wednesday night.
Washington cut it to4-1 on a power-play goal by Joel Ward, whose shot appeared to deflect off newcomer Andrew MacDonald. After two periods, the Caps had been outshot, 23-8.
After the trade deadline passed and the Flyers had made just one minor move Wednesday afternoon, general manager Paul Holmgren said he deliberately didn't shake up the team.
"They've been through a lot together - the poor start, the coaching change - and they've battled back, and I think they deserve to stick together and see where they can go," Holmgren said.