DENVER — Mikko Rantanen missed training camp and the preseason, yet showed he hasn't missed a beat after a summer of uncertainty.

Rantanen had two goals less than a week after agreeing to a contract with Colorado, Joonas Donskoi scored twice in his debut and the Avalanche beat the Calgary Flames 5-3 on Thursday night.

It capped a wild few days and nearly 5,000 miles of travel for the 22-year-old Rantanen.

"Everything happened really quick. I got a call last Saturday and now I'm here," Rantanen said. "It's already been four or five days and played the first game, too. I felt surprisingly good; it's probably going to take a couple of games to get fresh legs."

Rantanen was a restricted free agent heading into the summer and he remained in his native Finland while contract negations dragged on through training camp. The parties finally agreed to a six-year, $55.5 million deal on Saturday night and Rantanen joined the team on Sunday, four days before the start of the season.

He had career highs in goals (31) and assists (56) in 74 games last season playing mostly with Nathan MacKinnon and Gabriel Landeskog on Colorado's top line. He didn't get to work with the team until Monday, but was sharp in more than 18 minutes of ice time against the Flames.

"As soon as I watched him practice for two days, 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."

Rantanen scored a go-ahead goal in the first period and added the eventual decisive score on the power play late in the second period, minutes after J.T. Compher gave Colorado a 3-2 lead.

Mark Giordano scored 16 seconds after Rantanen's second goal but the Flames couldn't overcome early penalties. Calgary had three in the first period and Colorado had two goals on six power-play chances overall.

"They got a lot of momentum and their top players got a lot of touches early," Giordano said of penalties. "It carried on for a while. I thought after the midway point of the game we did a better job. When we were 5-on-5 we were very good."

Johnny Gaudreau and Sean Monahan each had a goal and an assist for Calgary. David Rittich had 26 saves for the Flames, who started the season the same way last season ended _ with a loss.

The Avalanche defeated Calgary in the first round of last season’s playoffs, beating the Western Conference's top seed in five games.

Donskoi got Colorado off to a quick start with a power-play goal 5:59 in, and the teams traded goals the rest of the period.

Gaudreau's goal 1:50 into the second period tied it and Donskoi scored into an empty net with 1:09 left in the third. Donskoi also helped the Flames when Monahan's shot deflected off of his stick and in for Calgary's first goal.

He made up for it with a strong debut after signing with the Avalanche on July 1.

"It felt amazing. I've been waiting for this moment all summer," Donskoi said. "There were a lot of emotions."

Colorado goalie Philipp Grubauer had 26 saves.

NOTES: Calgary LW Milan Lucic was given a game misconduct late in the second period. ... The Flames announced Thursday they had signed general manager Brad Treliving to a multi-year contract extension. Treliving is in his sixth year as the club's GM. ... Avalanche D Conor Timmins made his NHL debut Thursday night. He was Colorado's second round pick in the 2017 draft. Fellow defenceman Cale Makar had an assist in his first regular-season game. Makar played in 10 playoff games last spring.

UP NEXT

Flames: Hosts Vancouver in their home opener Saturday night.

Avalanche: Host the Minnesota Wild on Saturday night.

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