John Tavares, Joe Thornton and Alexander Kerfoot, into an empty net, also scored for Toronto, and Jack Campbell made 25 saves. The Maple Leafs stretched their North Division lead to eight points over the second-place Jets.
''We didn't lay back,'' Marner said. ''Everyone was ready for the challenge.''
Thornton, at 41 years, 296 days, became the oldest player in Toronto franchise history to score. He broke the record set by Allan Stanley at 41 years, 252 days on Nov. 8, 1967.
''Really liked the contribution all throughout the lineup,'' Toronto coach Sheldon Keefe said. ''Four lines, six defensemen all contributing in various ways for whatever the game called for. ''Just a solid team win. It's what it takes when it counts the most.''
Nikolaj Ehlers scored for Winnipeg, and Connor Hellebuyck stopped 33 shots. The Jets have lost three straight for the first time this season.
''This is going to be a big character build for us,'' Hellebuyck said. ''You never know how much adversity you go through, and we seem to keep going through little spurts of adversity. Hopefully, we come back from this stronger.''
Toronto improved to 6-3-0 against the Jets this season, including a 4-0-0 record in Winnipeg. The Maple Leafs have won two straight after dropping five in a row (0-3-2).
''Just two good teams going at it,'' Thornton said. ''Neither team wants to back down.''
Maple Leafs: Host Montreal on Wednesday night.
Jets: Host Edmonton on Monday and Wednesday night.
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