Matthews made it 4-2 with the Maple Leafs' third power-play goal at 15:05. He scored his NHL-leading 18th goal with a low wrist shot from the top of the left face-off circle that went in off Price's right pad.
"They had three power-play goals tonight, that's the difference in the game," Byron said. "If we get the kills, it's a completely different game for us. And that's just part of your job. We've got to find a way to be better."
A Montreal goal was disallowed at 15:29 of the second period. A video review confirmed the puck crossed the goal line, but a subsequent challenge by Toronto determined that Kotkaniemi's stick pushed Andersen's pad.
Alex Kerfoot scored at 13:36 of the third period for a 5-2 lead. Toffoli made it 5-3 at 18:34.
"I didn't like the chaos that was the second period," Maple Leafs coach Sheldon Keefe said. "Once we got our lead, we've got to do a better job with that. In the third period we were really good in that regard and we just sucked the life out of the game, which is what you want to do when you've got a lead against a team like this, especially a fresh team that we knew was going to have lots of legs in the third period.
"We needed to slow the game down, and the guys did a good job of that."
NOTES: Matthews did not play in a 4-2 win at the Edmonton Oilers on Jan. 22 and has scored 24 points (16 goals, eight assists) in the 13 games since. … Matthews scored the first goal for a fourth straight game. He is the 12th NHL player to do that, the first since Andre Burakovsky scored first in four consecutive games for the Washington Capitals from Jan. 15-21, 2017. No one has done it in five straight.