Ovechkin, who scored 14 goals in his prior seven games, remained two goals from becoming the eighth NHL player to score 700.
"It was not a good night," Washington coach Todd Reirden said. "So it's up to us to get away from the rink tomorrow and be back ready to play another [Metropolitan Division] opponent and see what our response is."
[WATCH: All Flyers vs. Capitals highlights]
Ovechkin, who had two shots on goal, will try again for 700 on Monday against the New York Islanders.
Claude Giroux reached 800 NHL points with a goal and two assists for the Flyers (30-18-7), who are 7-2-1 in their past nine games.
"The win feels the best, especially when you come to a building that's really tough to play in, and I haven't been playing that great lately," said Giroux, who had not scored a goal in 13 games. "It's good to be able to contribute to a team win and we have to keep it going."
Brian Elliott made 25 saves for Philadelphia, which lost to the New Jersey Devils 5-0 on Thursday.
"There's no doubt that our guys were highly motivated, but I think we were motivated against the Devils. Tonight, the difference was we were able to capitalize on some of our looks," Flyers coach Alain Vigneault said. "We had the saves at the right time. But go figure it out: We were able to put seven tonight and we weren't able to put one last game."
T.J. Oshie and Evgeny Kuznetsov scored for the Capitals (36-14-5), who are 2-3-0 in their past five games. Braden Holtby was pulled after allowing seven goals on 25 shots. Ilya Samsonov made one save in the final 11:58.
"In all areas, we lost every aspect of the game tonight," Reirden said. "And when you're going to do that in this league against a divisional opponent, then you're not going to have success."
The Flyers took a 1-0 lead on Sean Couturier's power-play goal at 15:22 of the first period. Giroux carried the puck behind the net and passed to Couturier, who scored with a one-timer from the left circle.
Video: PHI@WSH: Couturier buries Giroux's dish for PPG
Oshie made it 1-1 with his 20th goal of the season, a one-timer from the slot during a power play at 18:18.
Nicolas Aube-Kubel skated around Radko Gudas and made a cross-ice pass to Michael Raffl, whose snap shot gave the Flyers a 2-1 lead at 2:45 of the second period. Couturier scored on a breakaway 14 seconds later to make it 3-1, and James van Riemsdyk increased the lead to 4-1 when he reached out with one hand on his stick and redirected Matt Niskanen's shot at 4:30.
"We didn't play smart, and at the start of the second with the puck we made some turnovers that cost us right away," Gudas said. "And right after each other, shift after shift. It swung the momentum their way."
Aube-Kubel made it 5-1 with a wrist shot from the left circle off a Capitals turnover at 2:58 of the third period, and the Flyers led 6-1 after Travis Konecny redirected Giroux's pass at 5:47.
"[Holtby] kept it as close as humanly possible for as long as possible, but, not executing, not choosing the right play, and I know I didn't think [it was] anything other than how bad we were playing and not anything to do with him," Capitals defenseman John Carlson said.
Video: PHI@WSH: Konecny scores on deflection to pad lead
Giroux's 5-on-3 power-play goal made it 7-1 at 8:02. Kuznetsov scored at 12:17 for the 7-2 final.
"It was important, especially after the last game," Couturier said. "This time of year, you really can't lose two, three in a row. It was important to come out of here with some points, and we got two, so it's huge."
They said it
"Really proud of the guys. I think we approached it the exact right way that we needed to. We acknowledged how embarrassing and how bad we were the other night and brought one of our best efforts of the season tonight. That's a good sign that we have a lot of character in here and something to build on." -- Flyers defenseman Matt Niskanen
"We're where we are in the standings (first in the Metropolitan Division), but I've said it and said it a number of times that we're not where we need to be. Tonight was a really good example of it. So, if you're going to lose in all areas of the game, then you're not going to pull out wins. We didn't deserve that win. We deserved what we got tonight." -- Capitals coach Todd Reirden
Video: PHI@WSH: Couturier makes pretty move for second goal
Need to know
Philadelphia finishes 2-0-1 against Washington this season. ... The Flyers had a 73-27 percent edge in face-offs. ... Niskanen, who played the past five seasons for the Capitals and was traded to the Flyers for Gudas on June 14, played his first game at Washington and received a standing ovation following a first-period video tribute. ... Capitals forward Carl Hagelin had his NHL career-high seven-game point streak end (three goals, four assists). ... It's Oshie's fourth 20-goal season in five seasons with Washington. He had one in seven seasons with the St. Louis Blues.
Flyers: Host the Florida Panthers on Monday (7 p.m. ET; ESPN+, NBCSP, FS-F, NHL.TV)
Capitals: Host the New York Islanders on Monday (7 p.m. ET; ESPN+, SNW, SNP, TVAS, NBCSWA, MSG+, NHL.TV)
Video: Flyers erupt for seven goals in win against Capitals