"It's a special way to get it. I'll remember this day throughout my whole life," Sundin said.
After the shorthanded goal, the Swedish star's teammates banged their sticks to ice to honor the accomplishment and the fans erupted in cheers when it was announced.
Sundin clapped his hands in honor of his fans.
"We have the best fans. The team hasn't won a championship since 1967. They don't want anything else than for us to do well," said Sundin, whose younger brother watched from the stands.
Sundin added an assist for the Maple Leafs, who have played four straight overtime games. Darcy Tucker and Alex Steen also scored for the Maple Leafs, who rallied after blowing a two-goal lead.
Tucker received a questionable hooking penalty with 8 seconds left in the third. Sundin skated up the ice in overtime and put a long slap shot past goalie Kiprusoff.
Sundin has 15 overtime goals in his career -- the most in NHL history
"It's only fitting that he scored that huge, big goal in overtime because he's done it so many times before for us," Tucker said. "It was nice to see the ovation from the crowd and all the guys sitting around waiting at the end of the ice. It was a very special moment for a lot of guys on the team."
"He was really going tonight," Iginla said. "It was an amazing shot on that last goal. Not many people would have stopped that. He got a screen and he got it all. You don't want to call it a nice goal, but it was impressive."
Mark Giordano scored twice for the Flames, who had just five goals in their first four games.
After Toronto defenseman Hal Gill turned the puck over in his end, Calgary's Daymond Langkow made it 4-4 at 7:15 of the third.
Calgary had a season-high four goals. That's usually enough for Kiprusoff, but Toronto capitalized on most of its chances -- something the Leafs have had trouble doing this season.
"This is a pretty tough building to play. There were a lot of penalties. They were scoring on power-plays," Kiprusoff said.
The Flames spent half of the first period in the penalty box, giving Toronto five power-play opportunities.
Tucker -- alone at the side of the net -- converted Kyle Wellwood's pass on the power play at 8:09 of the first.
After defenseman Bryan McCabe faked a shot just over a power play expired, he passed to Sundin, whose one-timer made it 2-0 at 15:09 of the first.
The Flames almost matched their goal total for the season with three straight goals in the second period.
Iginla made a pass from behind the net to Giordano, whose wrist shot cut it to 2-1 at 11:26 of the second.
Tony Amonte's shot deflected off the boards behind the net to Matthew Lombardi, who scored a short-handed goal from the side of the net at 7:53.
Giordano gave Calgary a 3-2 lead by skating toward the net untouched before putting a backhander past goalie Andrew Raycroft at 11:26.
Steen poked the puck past a sprawled Kiprusoff at 17:38 of the second.
Just over a minute later, Raycroft made a spectacular kick save before Sundin staked up the ice and put a wrist top shelf, blocker side.
Toronto outshot Calgary 43-30. ... Calgary has scored one goal in 32 power-play chances this season. ... Toronto forward Michael Peca missed the game with a lower body injury. ... Raptors general manager Bryan Colangelo and assistant general manager Maurizio Gherardini sat behind Toronto's bench.
Copyright by STATS LLC and The Associated Press
Arena: Air Canada Centre Location: Toronto, Ontario
Referees: Tim Peel, Justin St. Pierre Linesmen: Ryan Galloway, Anthony Sericolo