Toronto was 0-for-7 on the power play.
"We didn't give up much on that 5-on-3 at all," Tkachuk said. "I really liked what I saw from the guys there. That's kind of what won us the game."
Monahan, who returned after missing two games with a lower-body injury, put the Flames up 3-0 at 3:26 of the third period when he scored on the power play.
Matthews had at least one point in 13 straight Toronto games, the longest such streak in the NHL this season, scoring 24 points (16 goals, eight assists) in that span. He did not play in a 4-2 win at the Edmonton Oilers on Jan. 22.
"We didn't really have a lot of jump to start the game, and they played very desperate tonight," Matthews said. "Things hadn't really been going the way they wanted to lately and they definitely came out with a purpose. We didn't really have any pushback."
Markstrom and Andersen each is day to day.
"Our guys are comfortable playing in front of David, they've got confidence in him, and obviously he's feeling it again, which is great," Calgary coach Geoff Ward said. "And it couldn't have come at a more opportune time for us and for him."
The Maple Leafs played without defenseman Jake Muzzin, who has a facial injury, and forwards Joe Thornton and Zach Hyman, each out with an undisclosed injury.
NOTES: Dan Bouchard was the other Flames goalie with a shutout in Toronto (April 2, 1975). ... Tkachuk reached 100 NHL goals at 23 years, 73 days old, which is 140 days faster than his father, Keith (23 years, 213 days).