Former Rangers forward Blair Betts scored 54 seconds into his return to Madison Square Garden, and Danny Briere and Claude Giroux took advantage of New York turnovers to push the Flyers' lead to 3-0 in the first period.
That was enough to end the night for goalie Henrik Lundqvist, who remained on the bench after the first intermission of his 300th NHL game. Lundqvist, who made his 13th straight start, sported a baseball cap and a dejected look as he watched warmups, shaking his head in the process.
Things went as well in the Philadelphia end as goalie Michael Leighton could have hoped. Leighton, claimed by the Flyers off waivers from Carolina on Dec. 15, made his fourth straight start and has won them all. Philadelphia is 4-0 on its six-game trip that will continue Friday in the Winter Classic at Boston's Fenway Park.
Leighton was hardly tested in earning his fourth NHL shutout, but first since Dec. 28, 2003. He had never won as many as three consecutive games before beating the New York Islanders on Sunday. The Flyers were on a 2-10-1 skid before this trip.
Chad Johnson was thrown into his NHL debut and was victimized on the first shot he faced. Gagne stole the puck from Brandon Dubinsky along the right-wing boards, skated in alone and beat Johnson just 23 seconds into the middle period.
Johnson settled down during the frame, and made a nice stop at the left post against Gagne, but he couldn't the Flyers at bay. During a 5-on-3 power play late in the period, Gagne turned a pass from Briere into another goal that made it 5-0 with 5:19 left in the second.
Philadelphia owned a 26-9 edge in shots at that point and helped turn the crowd against the host Rangers. When fans weren't booing or chanting for general manager Glen Sather to be fired, they were cheering announcements that there was only one minute left in the noncompetitive first two periods.
Gagne finished his third NHL hat trick with 8:30 remaining. He has four goals and three assists in six games since returning from abdominal surgery.
Betts' last appearance with the Rangers was a Game 6 loss to Washington in the first round of last season's playoffs when then Washington enforcer Donald Brashear - now a member of the Rangers - drilled him with a hard hit that left Betts with broken bones in his face.
He had reason to celebrate early in his return when he got to a rebound in front and scored past Lundqvist despite being surrounded by four Rangers.
Several minutes later, following a turnover by defenseman Marc Staal, Mike Richards set up Briere's 14th goal of the season at 8:09. The already frustrated Lundqvist banged his stick against the crossbar.
It would only get worse.
Gagne smacked the puck from the left circle into Lundqvist, and the rebound came right to Giroux - who scored an uncontested goal from the slot with 6:32 left in the first. That prompted fiery coach John Tortorella to use New York's lone timeout and yell at his club that had earned points in five straight games (4-0-1).
The Rangers were outshot 11-5 in the period, 29-10 through 40 minutes, and 31-22 overall.
NOTES: Richards and Flyers defenseman Chris Pronger were selected to the Canadian Olympic team Wednesday. Richards has four goals in three games after going seven games without one. Jeff Carter, who had two assists, was left off the Canadian squad. ... The Rangers' previous worst loss of the season was an 8-3 defeat at Pittsburgh on Nov. 28. ... Lundqvist has been pulled from two games this season.