Gagne, Darroll Powe and Ian Laperriere and each had a goal and an assist to help the Flyers win their fourth straight and send the Stars to their eighth straight road loss with a 6-3 win Tuesday night.
The Flyers credited the system of new coach Peter Laviolette, who replaced John Stevens as coach on Dec. 4.
"It's an aggressive system and allows players to shoot," Powe said. "That's what we like doing. Skating, getting in on the forecheck, hitting guys. It plays well into my game."
Steve Ott scored twice and James Neal added the other goal for the Stars, who last won on the road at San Jose on Dec. 11 in a 3-2 shootout.
"We gave them every opportunity to take over the game and they did," Dallas center Brad Richards said. "We've been self-destructing, shooting ourselves in the foot. No one's trying to do this stuff, but we're doing it."
Philadelphia's Michael Leighton made 27 saves. Leighton has started 10 straight games and has gone 8-0-1.
"It's not going to happen every game but we're playing well offensively and defensively right now," Leighton said.
Hartnell got the Flyers on the board at 6:08 of the first period, scoring on a backhanded flip over Dallas goaltender Marty Turco on a power play.
Neal scored his team-leading 19th goal off a give-and-go with Loui Eriksson 56 seconds into the second period.
The Flyers then struck back with four goals in the next 10:28 to take a 5-1 lead and chase Turco, who stopped only 14 of 19 shots. Alex Auld had eight saves.
Powe started the barrage after taking a pass from behind the net from van Riemsdyk at 2:32. Timonen scored shorthanded at 7:53, Giroux at 12:01 when his shot kicked off the right foot of Dallas defenseman Mark Fistric, and Laperriere 59 seconds later.
"Scoring comes from every line now and that's usually a good sign," Timonen said. "Hopefully we can keep it going."
Gagne scored after taking a cross-ice pass from Danny Briere at 10:55 of the third period. Ott scored from the crease at 12:47 and again at 16:06 on a rebound.
Philadelphia D Danny Syvret sustained an upper body injury early in the first period and did not return. ... Dallas is 0-for-22 on the power play in its last five games. ... The Flyers have scored first in ten straight games.
Copyright by STATS LLC and The Associated Press
Arena: Wells Fargo Center Location: Philadelphia, Pennsylvania
Referees: Stephen Walkom Linesmen: Andy McElman, Tim Nowak
Attendance: 19,133 (98.1% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Scott Hartnell (11)
(Power Play) Assists: Matt Carle, Jeff Carter
James Neal (19)
Assist: Loui Eriksson
Darroll Powe (8)
Assists: James van Riemsdyk, Arron Asham
Kimmo Timonen (4)
(Shorthanded) Assists: Ian Laperriere, Chris Pronger
Claude Giroux (10)
(Power Play) Assists: Simon Gagne, Matt Carle
Ian Laperriere (3)
Assists: Darroll Powe, Daniel Carcillo
Simon Gagne (6)
Assists: Daniel Briere, Mike Richards
Steve Ott (8)
Assists: Jere Lehtinen, Trevor Daley
Steve Ott (9)
Assists: Stephane Robidas, Matt Niskanen