Riding Kessel's three-goal performance, Toronto recovered from a poor start to defeat Anaheim 4-2 and deny the Ducks a club-record eighth straight win.
It was a Jekyll and Hyde performance for the Leafs, who were booed off the ice after a woeful first period that saw them outplayed, outshot 6-2 and outscored 1-0. Kessel struck twice and Toronto scored three unanswered goals in the second period to climb out of a 2-0 deficit.
"The first period we were awful tight," said Toronto coach Randy Carlyle. "We couldn't execute a 20-foot pass if the guy was wide-open ... We were tripping over one another the first period."
Toronto got its forecheck going and Kessel started the comeback with a power-play goal at 7:44 of the second period. The Ducks began to unwind and the Leafs led 3-2 going into the third.
Anaheim coach Bruce Boudreau was left lamenting the sudden turnaround.
"We played really good for the first 30 minutes of the game. I mean, as good as we can play," he said. "But I think the big thing is we just lost our composure for 10 minutes. And we've got to get it back. We'll get it back in practice (Wednesday).
"Nobody likes losing. Especially in this building. But we'll get out of it."
Captain Dion Phaneuf also scored for the Leafs (7-3-0) before an Air Canada Centre crowd of 19,408.
James van Riemsdyk, who played provider to Kessel most of the night, had a chance to make it 5-2 in the third period but hit the goalpost with a backhand on a penalty shot after being interfered with on a breakaway.
Kessel, whose offence had been sporadic this season, upped his goal total to five with the hat trick. The Leafs winger had a chance to go for a fourth late in the game but chose to pass it to linemate Tyler Bozak, who failed to convert.
The Leafs star came into the game with two goals on 36 shots. He left with five on 40.
Nick Bonino and Mathieu Perreault scored for Anaheim (7-2-0).
The win snapped a two-game losing streak for the Leafs and Carlyle, who led the Ducks to the Stanley Cup in 2007 before being fired in 2011.
Tuesday's game was the first stop on a season-long eight-game road trip for the Ducks, a journey that will cover 15 days and 13,215 kilometres.
Anaheim outshot Toronto 25-23.
Shots have been hard to come by for the Leafs, who were outshot 115-60 in their three previous games. Toronto has been outshot in eight of 10 games this season, including its last seven outings.
Neither team showed much in a loose first period that saw Toronto register its first shot 27 seconds in and then not put another on Jonas Hiller until an easy long-range shot from defenceman Paul Ranger with 2:56 left in the period.
Thirty-four seconds later, Bonino tapped in a pass from Patrick Maroon on a three-on-one after Leafs defenceman Cody Franson collided with teammate Troy Bodie up ice. It was Bonino's fourth of the year.
Carlyle's advice to his tense team after the first period was to relax and "go play."
Still stuck on two shots, Toronto went down 2-0 at 1:59 of the second period after Perreault was allowed to come out from behind the goal and roof a wrist shot past Jonathan Bernier for his fourth of the year.
Toronto did not manage a third shot until 5:23 of the second period, a snap shot by Jay McClement that produced a fine glove save from the underemployed Hiller. The Ducks goalie then stopped Mason Raymond on a two-on-one as the Leafs managed to move the shot clock again.
Phaneuf tried to start something at the other end, getting the crowd going by sending Kyle Palmieri flying with a bodycheck.
The Leafs finally scored in the second period with Kessel tucking in the puck on the power play after van Riemsdyk stretched to pass a rebound over to his unmarked linemate for his third goal.
Phaneuf then tied it up at 9:03, cruising in from the blue-line to bang home a rebound for his second of the season.
The dazed Ducks called a timeout to regroup.
Toronto had to survive an 87-second five-on-three power play later in the period.
Kessel scored again after Ranger dispossessed a Duck and sent his winger off on a two-on-one with van Riemsdyk. Kessel held onto the puck and beat Hiller at 16:09 for a 3-2 lead and his fourth goal of the campaign.
The shot count was tied 12-12 after two periods with Bernier making some timely stops in the third.
Kessel made it 4-2 at 8:11 of the third, effortlessly converting a two-on-one with van Riemsdyk.
"JVR made two great passes to me and I was fortunate enough to bury both of them," Kessel, who signed an eight-year, US$64-million contract extension earlier this month, said in a pithy assessment of his evening.
"It was a good night," he concluded.
Phaneuf was more effusive.
"Those were some serious goal-scorer goals," said an admiring skipper. "He didn't have a lot of room on two out of the three and he found away to put the puck in the net. That's what he does, that's why he's one of the top players in the league.
"It's a huge game by him for our team."
It was the Ducks' first defeat since a season-opening 6-1 loss in Colorado. Anaheim arrived in Toronto on a seven-game win streak, tied for the longest in club history (set previously between Feb. 20 and March 7, 1999).
The loss dropped the Ducks' record at Air Canada Centre to 3-12-4 and Hiller's career mark against the Leafs to 0-4-0.
The last time the two clubs met, a 5-2 Toronto win at the Honda Center on Nov. 27, 2011, Carlyle was behind the Ducks' bench. He was fired three days later and replaced by Boudreau.
NOTES — Steve Yzerman and Peter Chiarelli of the Canadian Olympic team braintrust took in the game ... Anaheim continues its road trip on Thursday in Montreal and Friday in Ottawa ... The Leafs will finally get forward David Clarkson back from his 10-game suspension on Friday in Columbus.