Juuso Valimaki and Elias Lindholm also scored for the Flames. Gaudreau and Lindholm each added an assist, and Jacob Markstrom stopped 24 shots. Calgary won its second straight to pull six points behind Montreal for the fourth and final playoff spot in the North Division.
Zach Hyman had a goal and an assist, Alexander Kerfoot also scored and John Tavares had two assists for the Maple Leafs, who lead the North by three points over Winnipeg. David Rittich had 25 saves in his Toronto debut two days after being traded by the Flames.
Toronto lost for the second straight night, comin off a 4-2 loss at Montreal on Monday to snap a 9-0-1 run. The Maple Leafs finished 6-2-1 in the season series against the Flames.
On the winner, Gaudreau took a pass from Lindholm and beat Rittich with a nice move for his 15th goal of the season.
The deal for Rittich — Toronto shipped a 2022 third-round pick to Calgary — was just one of the trades made ahead of Monday’s deadline by Maple Leafs general manager Kyle Dubas, whose other moves included acquiring forwards Nick Foligno and Riley Nash from Columbus, and defenseman Ben Hutton from Anaheim.
The Flames snapped a 1-1 tie 34 seconds into the second period with Mitch Marner in the box for tripping when Lindholm took a pass from Matthew Tkachuk and wired his 11th past Rittich.
Markstrom made his best save of the night early in the third with a desperation effort at full stretch on Marner, but the Leafs tied it at 6:17 when Kerfoot scored his seventh off a pass from Tavares.
The Leafs’ power play — an inexplicable 1 for 36 over Toronto’s last 15 games — got its first chance midway through the period when Rasmus Andersson was assessed a double-minor for high-sticking, but couldn’t generate much of anything until Tavares hit the post late in the man advantage.
Calgary, which beat the Edmonton Oilers 5-0 on Saturday to snap a 1-8-0 slide before dealing center Sam Bennett to Florida ahead of the deadline, opened the scoring at 4:37 of the first when Lucic found a wide-open Valimaki in front to score his second.
Toronto got even at 10:37 when Morgan Rielly’s shot off the end boards bounced to Hyman for him to pop his 15th upstairs on Markstrom. Rielly’s assist was the 300th point of his career, making him the sixth Toronto defenseman to reach that mark.
Flames forward Milan Lucic played in the 1,000th regular-season NHL game of his career. Lucic, who took a couple solo laps in warmups before being joined by teammates, got an ovation from both benches during the first TV timeout to acknowledge the milestone.
“I’ve been fortunate enough to have some special people in my life,” Lucic, the 50th pick in the 2006 draft by Boston, said after the morning skate. “You’ve got to live in the moment, you’ve got to enjoy the moment.”
Rittich, who blanked his new team 3-0 on Feb. 22 at Scotiabank Arena and had a .941 save percentage in four starts against the Leafs, flew on the Flames’ charter to Toronto on Monday because of COVID-19 restrictions related to commercial travel.
“There was definitely some fun happening there as far as pokes and jabs,” Lucic said with a smile Tuesday morning. “With the circumstances, you don’t ever really experience something like that ... flying with an ex-teammate or somebody on another team.
“It was kind of nice and cool to have around for a little bit (longer) and be able to properly say goodbye.”
Flames: At Montreal on Wednesday night to open a two-game series.
Maple Leafs: Host Winnipeg on Thursday night to wrap up a two-game homestand before a six-game road stretch.