Sundin blasted a slap shot from just inside the blue-line that rocketed past Vezina Trophy winner Miikka Kiprusoff, a short-handed goal by the Leafs captain that had 19,338 fans jumping out of their seats at the Air Canada Centre.
The fans stood on their feet and yelled their support for the 12-year Leaf, who was also named the game's first star thanks to a hat trick that also featured his 498th and 499th career goals. A magical night indeed in Toronto.
Alexander Steen and Darcy Tucker also scored for the Maple Leafs (3-1-2), who were missing checking centre Michael Peca, out day to day with a lower body injury.
Mark Giordano had his first two career goals for Calgary, while Matthew Lombardi and Daymond Langkow also scored for the Flames (2-2-1), who lost despite scoring a season-high four goals. They had entered the game with only five goals in four previous games.
The Leafs deserved the victory, outshooting the Flames 43-30, but getting only average goaltending from Andrew Raycroft, who got the win despite allowing four goals.
Tucker, with his team-leading fifth goal of the season, opened the scoring 8:09 into the first period, sliding in a perfect cross-crease pass from Kyle Wellwood during a Leafs power play. The backdoor play between Wellwood and Tucker has become all too familiar early in this season and one opposing teams will start to pick up in their video sessions.
Sundin made it 2-0 with 4:32 left in the opening period just as a 5-on-3 power play was ending, blasting a one-timer in an open side after a fake shot and pass by Bryan McCabe.
Calgary cut the lead to 2-1 at 4:52 of the second period, a goal coming with the Flames totally outplayed, the rookie Giordano scoring his first career NHL goal in his hometown of all places, beating Raycroft with a wrist shot from the high slot that rang in off the post.
The Leafs continued to carry the play but the Flames tied it 2-2 with a short-handed goal, Lombardi stuffing a loose puck under a sprawled Raycroft at 7:53 of the second period. The score was tied despite Toronto outshooting Calgary 22-9 at that point.
The goal gave the Flames some wind in their sails and Giordano continued his dream-like evening, shooting out from the Leafs corner and scoring on a backhand deke that beat Raycroft between the legs at 11:26 to give Calgary a 3-2 lead that wasn't exactly deserved.
The Leafs then tied and went ahead with two goals 1:10 apart, Steen scoring with 2:22 to go in the middle period, poking in a loose puck while falling down and Sundin beating Kiprusoff with a wrist shot that deflected off the stick of Giordano.
Langkow pulled Calgary to 4-4 at 7:15 of the third period, his wrist shot from a tight angle somehow beating Raycroft over his right shoulder.
Notes: In honour of Pink Ribbon Night at the Air Canada Centre, players on both teams wore pink decals on their helmets in support of the fight against breast cancer ... The two clubs won't face each other again this season ... Blue-liner Rhett Warriner (knee) is Calgary's only injury. Winger Darren McCarty was a healthy scratch but the diehard Detroit Tigers fan was elated after watching his ball team make it to the World Series with a Game 4 win. "I was there in '84 when they last won the World Series. It's a long time coming," said McCarty ... Brenden Bell made his season debut after returning from a foot injury. His addition on the blue-line pushed tough guy Wade Belak back up to forward ... Outside of Peca, defencemen Pavel Kubina (knee), Andrew Wozniewski (shoulder), Carlo Colaiacovo (head), Staffan Kronwall (ankle) and forwards Ben Ondrus (contusion) and Nik Antropov (leg) were out for Toronto ... The Leafs next host Colorado on Wednesday while Calgary is at Montreal on Tuesday.