Nathan MacKinnon had two assists to extend his point streak to nine games (four goals, 12 assists) and Samuel Girard had three assists for the Avalanche (28-13-3), who are 4-1-0 in their past five games. Jason Polin scored his first NHL goal and Justus Annunen made 36 saves in his season debut.
Colorado scored five straight goals after being down 4-2 midway through the second period. The previous time the two teams met on Dec. 21 the Avalanche scored four straight goals after being down 4-2 en route to a 6-4 victory.
Ridly Greig scored twice, Jake Sanderson had a goal and an assist, and Brady Tkachuk and Claude Giroux each had three assists for Ottawa (15-24-0), which is 1-6-0 in its past seven games. Mads Sogaard made 27 saves in his season debut.
Drake Batherson gave Ottawa a 1-0 lead at 9:29, scoring on his own blocked shot in the slot on the power play.
Rantanen tapped in a centering pass from Cale Makar to tie it 1-1 at 10:07. Rantanen also has a nine-game point streak (14 points; six goals, eight assists).
Greig gave the Senators a 2-1 lead at 1:21 of the second period. Tkachuk’s point shot hit the post and the puck laid on the goal line until Greig dove and poked it in.
Polin elected to shoot on a 2-on-1 and beat Sogaard glove side with a snap shot to tie it 2-2 at 2:27.
Greig scored his second goal of the period to make it 3-2 at 7:21 when he took a centering pass from Tkachuk, skated into the slot and beat Annunen with a wrist shot blocker side.
Sanderson made it 4-2 at 11:04 when he drove to the net and finished a deke on the forehand in tight.
The Avalanche thought they’d scored when Sam Malinski beat Sogaard with a curl-and-drag wrist shot from the top of the slot on the rush at 15:15. But Ottawa challenged, and the goal was overturned when video review determined Jonathan Drouin was offside.
Rantanen took a cross-ice pass from MacKinnon on the rush and scored with a snap shot top right from just inside the left face-off dot to cut it to 4-3 at 16:18.
Miles Wood beat Vladimir Tarasenko wide, cut to the middle and chipped the puck over Sogaard’s blocker to tie it 4-4 at 4:04 of the third period.
Malinski put Colorado in front 5-4 at 8:14 with a wrist shot from the point that beat Sogaard clean on the power play.
Logan O’Connor used Sanderson as a screen and beat Sogaard glove side with a wrist shot from the slot to make it 6-4 at 12:24.
Devon Toews scored into an empty net for the 7-4 final at 15:16.