Lehkonen finished a cross-crease pass from MacKinnon on a 2-on-1 at 11:01 to make it 2-0. He scored 1:57 later to extend it to 3-0 with a power-play goal after a point shot by MacKinnon went off Rantanen and the end boards to him at the left post at 12:58.
"Obviously, we didn't come out ready to go and they did," Toffoli said. "They were faster in all areas of the ice -- skating, passing, and everything. We were trying to find our way back into the game, but they're the defending [Stanley Cup] champions for a reason."
Toffoli shot through a screen by Lindholm from the top of the left circle on a power play to cut it to 3-1 at 2:27 of the third period.
Colorado was outshot 13-4 in the third.
Georgiev made a save on Blake Coleman at the edge of the crease at 8:52 before stopping him again on a partial breakaway after he split the Avalanche defense at 9:24. Georgiev also made a glove save on a backhand by Trevor Lewis in the slot at 11:47.
"Really good," Rantanen said. "They were pushing hard. We gave up some chances, but [Georgiev] was calm and cool in the net. Really, really good performance by him."
Rantanen was awarded a goal at 19:02 after he was slashed on a breakaway by Flames defenseman Nikita Zadorov with Markstrom pulled for an extra attacker for the 4-1 final.
"Honestly, when you come out like that in the first against the champs, it's not gonna work very well," Lindholm said. "You can't expect to win when you play like that. So, obviously, that first period set the whole game up."