MacKinnon put the Avalanche ahead 2-0 at 3:24 of the second period, one minute after Lundqvist made a glove save against Alex Kerfoot on a breakaway. MacKinnon skated from left to right and beat a lunging Lundqvist to the glove side for his 23rd goal. It was the fifth straight game he's scored.
"I was looking to pass and I didn't see anything," MacKinnon said. "I just got to the middle of the ice and tried to use some bodies as a screen, keep it low. I'm not really picking a spot there, just trying to get it through."
It was MacKinnon's seventh game-winning goal this season. He ranks second in the NHL with 59 points, two behind Nikita Kucherov of the Tampa Bay Lightning.
"If I was feeling pressure (to carry the load) I don't think I'd be producing like this," MacKinnon said. "Gabe (Landeskog) and Mikko and everyone else makes it really easy. I think we're top three or four in the League scoring, and that's not just from me, it's from everybody. When Bernier is playing as well as he is, it takes a lot of pressure off us to score."
The Rangers got to within 2-1 at 6:55 of the second on a power-play goal by Buchnevich, who deflected in Mats Zuccarello's shot for his 13th goal.
Rantanen scored an empty-net goal with less than one second remaining in the third to make it 3-1.
"Our guys are hungry to keep it going," Avalanche coach Jared Bednar said. "It means a lot to them and it's showing in their play and what they're saying to each other on the bench. I'm really happy with what I'm seeing right now."