"We had an awful start," Coburn said. "We can't start hockey that way."
The Maple Leafs took advantage of shaky play from Mason and took a 1-0 lead. After Troy Bodie drove the net and put the puck on Mason, the Flyers were unable to clear it from in front.
Sneaking in from the blue line, Gardiner shot through a screen set by Frazer McLaren and ex-Leafs defenseman Luke Schenn, and past Mason at 2:21 of the first.
It took only a minute after Gardiner's goal for the Leafs to add to their lead.
Lupul skated into the offensive zone and dropped the puck to Kadri, whose wrist shot beat Mason at 3:38. It was Kadri's 17th goal, one short of his career high set in 48 games last season.
Mason stopped the next 29 shots he faced, including a highlight-reel sliding save on Phil Kessel early in the third.
"He held us in there," Flyers coach Craig Berube said. "I thought he did a real good job, made some big saves. They're a good offensive team, they make plays and he came up big."
The Leafs might have caught a break early in the second period when it appeared that Matt Read scored for Philadelphia. After a quick consultation with the other officials, referee Kevin Pollock waived it off and announced that Bernier had the puck covered.
Bernier was beaten for real at 18:02 of the second. Receiving a pass from Jakub Voracek, Timonen skated to the top of the left circle and snapped a shot in. It was the Finnish Olympian's first goal in 30 career games against Toronto.
Bernier was helpless to stop the Flyers' second goal after Voracek skated behind the net and sent a pass through Toronto defenseman Tim Gleason to Timonen in front. He flipped a backhander over Bernier at 7:19 of the third to make it 2-2.
Raymond made it 3-2 at 13:34 when his shot hit the post and then the back of Mason's right pad. Bodie appeared to knock the puck in by hitting the pad, but he never touched it.
Toronto blew another third-period lead at 17:28 when Coburn's shot through traffic managed found its way past Bernier.
Lupul ended it in overtime, finishing a tic-tac-toe passing play involving Carl Gunnarsson and Dion Phaneuf.
NOTES: Forward David Clarkson was scratched for the Maple Leafs because of a pulled muscle sustained Friday in practice. D Paul Ranger was a healthy scratch as McLaren was called up so the Leafs could dress 12 forwards. ... Steve Downie was scratched for the Flyers because of the flu. Ex-Leafs forward Jay Rosehill took his place.