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.
“The penalty-killing did a good job there, the power play scored a big goal for us,” Flames coach Darryl Sutter said. “That second period was real tight checking. We knew they are the best team in the league, they're going to push in the third and they did and we hung on.”
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.
“It was tough,” Rittich said of playing his old teammates. “I’ve got some (life-long) friends there.”
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.
“We've had a couple of shootouts in the last few practices before the (trade) deadline there, scored a couple on him,” Gaudreau said of his former teammate. “I kind of felt a little comfortable there. I normally don't go to my forehand, and I think I kind of fooled him a little bit there.”
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.
“He’s been great, loves to chat,” Tavares said of Rittich, who gave Jack Campbell a breather. “Quite the circumstances the last 48 hours for him. Probably the main reason we got a point.”
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.
“That was a kill for us,” Gaudreau said. “They've got some talented players over there on their side so to be able to kill off four minutes late in the third there was really impressive, and some great saves from Marky in the third on that PK.”
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.
“Personally, it's a great achievement," Lucic said. “It makes it that much better when you get a big win. ... It adds so much more to it especially when we're desperate for wins and we get a big win like that against the best team in our division.”
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.
“It was OK, a lot of chirps,” Rittich said of the strange circumstances. “Some guys didn’t hold back. ... But at least I had a chance to say goodbye to all of them.”
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.