Nathan MacKinnon had three assists, and Tomas Tatar and Devon Toews had two assists for Colorado (9-5-0), which had lost three of their past four games. Alexandar Georgiev had 18 saves.
Brandon Tanev scored his first of the season for Seattle (5-8-3), which had won its past two games. Joey Daccord made 26 saves.
Tanev tucked in a rebound off a point shot from Vince Dunn to make it 1-0 at 6:13 of the first period.
Alex Wennberg appeared to extend the lead to 2-0 at 14:41 with a short-handed goal, but a video review determined that Tanev interfered with Georgiev.
Rantanen tied it 1-1 at 12:05 of the second period when he tapped in a rebound from the crease into an open net.
Ross Colton gave the Avalanche a 2-1 lead with a power-play goal at 14:12, putting in a rebound past Daccord’s right pad.
Makar pushed it to 3-1 with a wrist shot from the top of the right circle at 4:14 of the third period after a give-and-go with Tatar.
Jonathan Drouin scored at 9:09 off a 2-on-1 rush with MacKinnon to make it 4-1. It was his first goal with the Avalanche after signing as a free agent on July 1.
Valeri Nichushkin deflected Makar’s shot past Daccord on a 4-on-3 power play for the 5-1 final.
