Florida took advantage of Toronto's defensive weaknesses in the third period though, scoring four unanswered goals on its way to a 6-4 come-from-behind win at BB&T Center.
The Panthers outshot the Maple Leafs 13-3 in the first period and 15-14 in the second, but after allowing four Toronto goals in the second, it took the big third period for Florida to rally for the victory.
Right wing Brad Boyes scored the game-winning goal with a little more than three minutes left to cap the comeback. Defensemen Dmitry Kulikov and Willie Mitchell scored 7:24 apart in the third to tie the game 4-4.
"They score a lot of goals, but they've also given up a few, so we said, 'You know what? If we get one, they're not great at defending leads,' and we got a couple bounces," Mitchell said. "My goal was a weak goal, and we kind of got the momentum going even more. But we did aggressively respond, and that's huge."
After a scoreless first period, Toronto and Florida combined for six goals in the second, and the Maple Leafs took a 4-2 lead into the second intermission.
But in the third period, the Maple Leafs couldn't keep the Panthers out of their zone, and Florida created more traffic in front of Toronto goaltender James Reimer.
"Playing the fundamentals of hockey has been a challenge for our group," Maple Leafs coach Randy Carlyle said. "It's just another example of we played too loose. You can't stop skating, and we stopped skating. We didn't execute with the puck."
Toronto took advantage of some sloppy defensive play by Florida to rack up four goals in the second period, three of which came in a span of 4:43.
"It was a total team thing in the second period on those goals," Florida coach Gerard Gallant said. "We made some bad mistakes. Guys had chances to get pucks out. And it's things we don't do usually, but we made up for it in the third.
"We had a good chat between periods. We talked about getting back to our game and playing it smart, and a north-south game, and fortunately for us, we got a couple of good bounces and got breaks, and I thought we worked hard and deserved to win the game."
Toronto right wing Richard Panik opened the scoring at 6:39 of the second. He grabbed the puck off the boards near the Maple Leafs bench, skated deep into the Panthers zone and beat Luongo short side for his seventh goal.
Huberdeau tied the game with his fourth goal 1:45 later. Seconds after Panthers defenseman Aaron Ekblad's shot from the point hit the post, Huberdeau pounced on a turnover in the Maple Leafs zone, then came in alone on Reimer and sent a high wrist shot over the Toronto goalie's right shoulder.
Hayes gave Florida the 2-1 lead less than two minutes later. He scored his 10th goal after taking a pass on a 3-on-2 from left wing Sean Bergenheim.
With 5:44 left in the second period, Toronto defenseman Roman Polak took a long pass from right wing Joffrey Lupul and put a wrist shot past Luongo, who was sliding to his right, for his fourth goal. Lupul's assist was his 400th career point.
Left wing James van Riemsdyk gave the Maple Leafs the 3-2 lead with 2:30 left in the second period on a power play. Center Tyler Bozak put the puck in front of the Panthers net, where van Riemsdyk got his stick on it and shot it over Luongo's extended right leg for his 16th goal.
Toronto center Nazem Kadri put the Maple Leafs up 4-2 with 1:01 left in the second period. Lupul came streaking down the left wing and put the puck in front of the Florida net. Kadri came straight in and beat Luongo glove side for his 11th goal.
Kulikov scored his first goal of the season on a one-timer at 2:45 of the third period to cut the lead to 4-3. He was left alone at the point with a lot of space.
Mitchell tied it with 9:51 left in the third on a slap shot from the left point. It was his second goal.
Boyes put Florida ahead 5-4 on a tip-in at 16:45 for his sixth goal, and Upshall scored an empty-net goal with 1:25 left.
"I think it's just one of those things where some pucks got by us in the net … unfortunately I just wasn't able to see a couple of them, and they wound up in the back of the net," said Reimer, who made 28 saves. "It's a case, from my standpoint, where I want to fight a little harder and smarter on my end to see the puck."
Reimer started after Jonathan Bernier was scratched with what the Maple Leafs called a flu-like illness.
The loss was a disappointing start to a five-game road trip coming off the holiday break for the Maple Leafs.
"The majority of the next practice days are going to be on defensive-zone coverage," Carlyle said. "That was our message even before tonight because of the last games that we've played. There's too much freedom in our zone. We're not doing enough pinning. We're not hard to play against in our defensive zone and we've got to become much different."
Toronto recalled goaltender Christopher Gibson from the Toronto Marlies of the American Hockey League to back up Reimer. To make room for Gibson, the Maple Leafs placed forward Leo Komarov on injured reserve retroactive to Nov. 29. Komarov, who sustained a concussion in Toronto's Nov. 29 game against the Washington Capitals, returned to practice Saturday.
The Maple Leafs said Bernier was not showing signs of the mumps.
Toronto right wing Carter Ashton returned to the lineup after serving a 20-game suspension for a positive test for performance-enhancing drugs. Ashton was sent down to the Marlies on Dec. 19 on a conditioning assignment before being recalled Saturday.