Morrissey's first goal of the season came on the fourth power play of the game for the Jets, who had failed to score on their previous 13 man-advantage opportunities. They finished 1-for-5.
"I thought we battled hard on that power play to get pucks back," Morrissey said. "There were a couple of good plays down low. We had talked right before that power play to try to get some shots to the net, get traffic there. When it's not going, that's usually a good recipe. Just was able to make a good shot, and you could see the double screen in front, I think [Mark Scheifele] and Kyle in front. When you have two screens like that and the goalie can't see, and you make a good shot, you can get rewarded."
Connor Hellebuyck made 29 saves for Winnipeg (6-6-0), which won for the second time in six games.
Elias Lindholm gave Calgary a 1-0 lead when scored on the power play at 14:17 of the second period, one-timing a pass from Johnny Gaudreau for his Flames-leading seventh goal.
David Rittich made 43 saves, an NHL regular-season outdoor game record, for Calgary (6-5-2), which has lost three of five.
"We played good for most of the night, and in the third period they came out strong, and we didn't have an answer for that," Flames forward Matthew Tkachuk said. "They get one late, and then they win in overtime on a 2-on-1. You know, they don't give you two points for playing well for most of the game, you have to finish it off."
The 2019 Heritage Classic was the 28th outdoor game in NHL history. It was the first at a neutral site of the seven played in Canada.
And it was one those involved said they would remember for a long time.
"Sometimes the best seat is right behind the bench because you can see it all," Winnipeg coach Paul Maurice said. "The fireworks are going off, and those jets come over, and [the national anthem] is just done, and it's snowing out. You just needed Santa and the reindeer blasting over, and it would make the perfect scene. It would have been about the only thing to top that one. It was really good, was what I was trying to say."