The rookie is rewarding their faith with a stellar first season.
Varlamov also had his second assist of the season.
Colorado is having a bounce-back season after finishing at the bottom of the Western Conference last year.
The decision has paid off. MacKinnon has 20 goals and 40 points to lead all rookies in scoring.
“I’ve been feeling more comfortable. I think I was a little snake-bit at the beginning and could’ve score more than I did,” said the 18-year-old MacKinnon, who had his first three-point game. “Thankfully things are clicking, I’ve developed chemistry with guys on the team.”
The Avalanche were playing their final home game before going on a four-game East Coast road trip ahead of the Olympic break. They have won eight of 10 and are 35-14-5. It’s their best start to a season since 2000-01 when they won the Stanley Cup.
Marc-Andre Cliche scored his first NHL goal and Tyson Barrie also scored for the Avalanche.
“We weren’t ready to go from the get go,” Buffalo coach Ted Nolan said. “We never laid a body on anyone. It was a very ugly game to watch.”
The Avalanche jumped ahead early and didn’t need to sweat out the end as they did against Minnesota on Thursday.
They scored three quick goals on Olympian Ryan Miller in the first. Barrie started the flurry with his seventh of the season at 7:37, and McGinn and Landeskog had goals 58 seconds apart later in the period.