Mark Jankowski had two goals and an assist, and Sam Bennett, Micheal Ferland, Johnny Gaudreau and Michael Frolik each scored for the Flames (10-7-0), who went 5-2-0 on their season-high seven-game homestand. Calgary will play its next six games on the road.
"It's a big win for us," Versteeg said. "We knew how good they've been playing. You don't think you're going to score that many goals against that team. It's definitely big for us."
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Lack relieved starter Mike Smith, who left after the first period because of an undisclosed injury. There was no update on Smith, who allowed two goals on nine shots.
It was Lack's first win for the Flames since being acquired in a trade from the Carolina Hurricanes on June 29. He has started one of 17 games this season.
"It's always different to practice," Lack said. "You can just go through the repetitions over and over and over again, but you can't really simulate the game. I'm hoping to get a little more consistency here."
Vladimir Tarasenko scored two goals, and Jaden Schwartz and Alexander Steen each had a goal and an assist for the Blues (13-5-1) in the first of their three-game Western Canada road trip. Jake Allen made 30 saves.
"We're going to have to reset everything and get back to the way we want to play, what we know is successful," Blues forward Paul Stastny said.