Gagne, who also scored in the first period, beat Tomas Vokoun after faking a shot and then deking to his backhand. Gagne scored on Philadelphia's second attempt after Mike Richards was stopped. Jeff Carter also scored in regulation for the Flyers, who had lost their last two. It was Philadelphia's NHL-high 17th overtime game of the season.
Bryan McCabe and Jay Bouwmeester scored power-play goals for the Panthers, who had their three-game winning streak snapped. Nittymaki made 32 saves in regulation and overtime while earning his first victory since Dec. 23. Vokoun, making his fourth straight start for Florida, stopped 24 shots.
The teams played a scoreless third period, although Florida's David Booth hit the post on a rebound from close range with just over 2 minutes left.
The Flyers took a 2-0 lead into the first intermission despite being outshot 15-12 in the first period.
Carter gave Philadelphia the lead at 12:12 with his NHL-leading 30th goal. Braydon Coburn's wrist shot from the high slot bounced off Vokoun's chest, and Carter put home the rebound.
Gagne made it 2-0 at 14:08 with a power-play goal. He fired the puck from the side of the net and it went off Vokoun's skate. Florida tied it in the second period when it outshot the Flyers 13-3, thanks in large part to four power plays.
McCabe cut the lead in half at 14:47 of the second period with a wrist shot from the point. McCabe's low shot went through defenseman Andrew Alberts and through the legs of Nittymaki.
A lucky bounce helped Bouwmeester tie it at 17:36. Cory Stillman's pass from behind the net went off the skate of Gagne in the slot and Bouwmeester grabbed the loose puck before firing a quick shot over the left shoulder of Nittymaki.
Notes: The Panthers haven't won a game all season when trailing by two goals. The last time they overcame a two-goal deficit was March 8, 2008, against Atlanta. ... Flyers D Kimmo Timonen, who left Thursday's game at Tampa Bay in the first period after being hit by a puck in the mouth, played with a facemask. ... LW Ville Peltonen was in the lineup for Florida, less than a week after breaking a bone in his right foot. ... Booth's career-high points streak was snapped at eight games.
