"I think we sent them a message that we're not going to accept it anymore," said Slava Kozlov, who savored his four assists after playing in eight straight losses to Toronto. "We beat them in our building and next week we get a chance to beat them in their building."
It was Atlanta's first win over the Maple Leafs since a 3-2 overtime victory on Oct. 27, 2003, in Toronto. The Maple Leafs outscored the Thrashers 37-9 in their eight straight wins, including a 4-2 victory on Oct. 30 in Toronto.
Hossa responded to Atlanta fans chanting his name by completing his hat trick with about 3 minutes left. Lehtonen earned his fourth shutout of the season, handing Toronto its first shutout loss.
"We're going to have some ugly nights, and this was one of them," Maple Leafs coach Paul Maurice said.
Lehtonen added to his team record with seven career shutouts, including two straight in home wins. He blanked Florida 1-0 on Saturday.
Toronto has totaled two goals in three straight losses, matching its longest skid of the season.
"Anytime you lose three games in a row it is frustrating, and we have a lot of work to do," said Mats Sundin, who led Toronto with six shots. "We have to get back. We're right in the mix of things and there are a lot of teams in the same position as we are, so we have to just start winning hockey games again."
Hossa ended his personal history of frustration against Toronto with his first hat trick for Atlanta. Hossa leads the NHL with 20 goals this season, but he had only one goal and one assist in his last nine games against Toronto, a streak that began before Hossa's 2005 trade to Atlanta from Ottawa.
Hossa passed the New York Rangers' Jaromir Jagr for the league scoring lead with 39 points. Hossa also leads the league with 20 power-play points.
"He's a fantastic player. He's awesome," Toronto's Jeff O'Neill said. "Give him time and space and he will hurt you."
Hossa said he heard the fans calling his name but said he wasn't thinking about completing his fifth career hat trick.
"It felt nice," he said. "If I get two goals or three goals that's fine, but I'm just happy the team won."
Hossa's first goal gave the Thrashers a 1-0 lead with 6:52 left in the first period. Hossa waited about five feet to Andrew Raycroft's left as the Thrashers crisply executed passes from Kozlov to Mellanby to Hossa, who was left with a clear opening for his short wrist shot.
Raycroft kept Atlanta's lead at 1-0 as he stopped breakaway attempts by Hossa in the first period and by Shane Hnidy early in the second.
Hossa and the Thrashers pushed the lead to 2-0 less than 2 minutes into the third period. Racing down the ice, Hossa took a pass from Kozlov with a skate, kicked it up to his stick and then scored on a snap shot in front of the net.
Jon Sim was called for slashing midway through the third period, but Toronto's Darcy Tucker and Hal Gill drew roughing penalties in their response to Sim, setting up a power play and two goals within 14 seconds for the Thrashers.
Mellanby scored the first on a pass from Hossa, and Larsen pushed the lead to 4-0 seconds later when he scored off Bobby Holik's assist.
The last Atlanta home win over Toronto came on Dec. 16, 2002.
- The Thrashers activated defenseman Steve McCarthy from injured reserve. McCarthy missed eight games with a shoulder injury.
- Toronto D Wade Belak drew a 4-minute penalty for high-sticking in the second period after sending Sim off the ice with an apparent hand injury. Sim returned.
- Mellanby scored his first goal in 14 games.
- The Thrashers improved to 9-0-1 when allowing no more than two goals.