Mark Giordano scored the winner and Jacob Markstrom made 24 saves as the Calgary Flames defeated the Toronto Maple Leafs 4-3 on Friday.
Matthew Tkachuk, Derek Ryan and Christopher Tanev scored for Calgary (15-13-3), while Rasmus Andersson added two assists.
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Mitch Marner, Jason Spezza and Alexander Kerfoot replied for Toronto (19-10-2), which has lost six of its last seven games in regulation.
The struggling Frederik Andersen stopped 14-of-18 shots for the Leafs, who will look to get back on track Saturday when the teams play their sixth of nine meetings this season back at Scotiabank Arena.
Toronto, which had four days off to reset between games after dropping a pair last weekend, had a nine-point lead atop the North Division standings on March 3, but were tied with the Edmonton Oilers on points — the Leafs had three games in hand — heading into Friday after dropping five of its last six.
The Winnipeg Jets, meanwhile, were two points back with the same amount of games played.
Sporting their white and green St. Pats jerseys, the Leafs got a boost with the return of Wayne Simmonds to the lineup after the gritty winger missed the last 18 games with a broken wrist.
Backup goalie Jack Campbell (leg) also suited up for the first time since Jan 24, while winger Alex Galchenyuk — the No. 3 overall pick in 2012 now with his seventh NHL organization since June 2018 — debuted for Toronto on a line with John Tavares and William Nylander.