DENVER -- Mikko Rantanen scored two goals for the Colorado Avalanche in a 5-3 win against the Calgary Flames in the season opener for each team at Pepsi Center on Thursday.
Rantanen signed a six-year contract Sept. 28 after missing all of training camp and the preseason as a restricted free agent.
"I can't deny, everybody loves to score goals, especially when the team wins," said Rantanen, who practiced with the Avalanche for the first time Monday after arriving from Finland on Sunday night. "It feels good. It's already been four or five days and now we played the first game. I felt surprisingly good, but it's probably going to take a couple of games to get fresh legs."
[WATCH: All Flames vs. Avalanche highlights]
Joonas Donskoi scored two goals, Cale Makar had an assist, and Philipp Grubauer made 27 saves for Colorado.
Sean Monahan and Johnny Gaudreau each had a goal and an assist, and David Rittich made 27 saves for Calgary, which has lost 10 straight season openers (0-9-1).
"The first 10 minutes in any team's building on their opener is always going to be that atmosphere that we had tonight," Flames defenseman Mark Giordano said. "They got a lot of momentum. Their top players got a lot of touches early. You touch the puck and it sort of carries on the rest of the game."
Donskoi scored a power-play goal to give the Avalanche a 1-0 lead at 5:59 of the first period, redirecting Samuel Girard's shot from just inside the blue line. Donskoi was making his Colorado debut after signing a four-year contract as a free agent July 1.
Video: CGY@COL: Donskoi deflects Girard's shot for PPG
Monahan tied it 1-1 with a power-play goal at 8:33 when his pass for Elias Lindholm, who was driving to the net, went in off Donskoi in front.
Rantanen made it 2-1 at 16:08 after he received a pass from Gabriel Landeskog and scored with a backhand from the right circle.
Gaudreau scored a power-play goal from the bottom of the right circle to tie it 2-2 at 1:50 of the second period off a cross-slot pass from Monahan.
J.T. Compher gave Colorado a 3-2 lead at 12:22 of the second, scoring into an open net after receiving a pass from Matt Calvert at the left post.
Rantanen scored his second goal on the power play for a 4-2 lead at 16:51. Nathan MacKinnon was in the left circle and sent a cross-ice pass to Rantanen, who gathered it before scoring top shelf.
"As soon as I watched him practice for two days (after signing his contract), I knew he was going to pick up where he left off," Colorado coach Jared Bednar said. "He came in and practiced and it looked easy for him. He's got a lot of confidence, he's happy with the new contract, and we're happy to have him back. He must have put in some good work in Switzerland for a couple weeks."
Video: CGY@COL: Rantanen snipes second goal on power play
Giordano cut it to 4-3 at 17:07 of the second, skating in from the left boards and scoring short side on Grubauer.
The Flames outshot the Avalanche 14-6 in the third period, including a breakaway by Monahan at 2:42 that Grubauer stopped.
"We had some moments 5-on-5, and the third period is a good example of that," Calgary coach Bill Peters said. "That was our best period and it's a period we stayed out of the box. We were able to get guys moving and skating, a little rhythm to the game."
Donskoi scored into an empty net with 1:09 left in the third for a 5-3 lead.
"It felt so good to get the win right away in the first game," said Donskoi, who spent his first four NHL seasons with the San Jose Sharks. "That was fun. It felt amazing. I've been waiting for this moment all summer."
Video: CGY@COL: Donskoi pots empty-netter for second goal
They said it
"Just too many penalties we took, it's pretty simple. It was hard to get into the groove of the game for everybody and then when your penalty killers are out there, they're working their tails off so they're pretty tired. And then guys who aren't on the penalty kill have a hard time getting in the game. It was kind of similar for both teams." -- Flames forward Matthew Tkachuk
"It was one of the weirdest games I've played in a long time. We gave up a couple shots (three) in the first period. As the game went on, I got more shots and I got more into the game. We knew they were going to push in the third and we handled it really well." -- Avalanche goalie Philipp Grubauer
Video: CGY@COL: Gaudreau whips puck in on the power play
Need to know
Calgary's last win in a season opener was against the Vancouver Canucks on Oct. 1, 2009 (5-3). … Colorado is 16-5-1 (with two ties) in home openers since moving from Quebec in 1995 and 4-0-0 in season openers under Bednar. … Avalanche defenseman Conor Timmins had one shot in 9:59 of ice time in his NHL debut. He missed all last season recovering from post-concussion issues. … Nazem Kadri, Andre Burakovsky, Pierre-Edouard Bellemare and Valeri Nichushkin each made his debut with Colorado.
Flames: Host the Vancouver Canucks on Saturday (10 p.m. ET; CBC, SNP, NHL.TV)
Avalanche: Host the Minnesota Wild on Saturday (9 p.m. ET; ALT, FS-N, FS-WI, NHL.TV)
Video: Rantanen, Donskoi propel Avalanche past Flames