LAS VEGAS (KLAS) — Sure, Tuesday’s second period, when the Golden Knights were penalized six times, hurt. They allowed two power-play goals, gave up a two-goal advantage and ended up losing 3-2 to the host Calgary Flames.

But Knights coach Bruce Cassidy cited a major flaw in his team’s first loss after opening the season with three straight victories.

“I don’t think we did enough in terms of net front battles in front of either net,” Cassidy said. “I think that’s where they were better than us in the long run.

“They were harder in front of their net, harder in front of our net.”

The best example came on the winning goal by Mikael Backlund with 4:29 remaining. Defenseman MacKenzie Weegar, in the high slot, rifled a shot high and wide, and Flames center Blake Coleman beat Knights defenseman Alex Pietrangelo to a loose puck behind the net.

Coleman shoveled a pass into the crease that Backlund jammed home. Neither defenseman Alec Martinez nor center Jack Eichel apparently felt an urgency to defend, allowing Backlund to roam free in front.

Bottom line: Two Flames beat three Knights in front of goaltender Logan Thompson.

Thompson was a bright spot again for the Knights with 37 saves, including a sprawling glove stop on Nazem Kadri — also roaming free in the slot — just before Backlund’s tiebreaker.

“He played unreal, gave us a chance to win,” defenseman Brayden McNabb said.

Tyler Toffoli and Elias Lindholm also scored for Calgary (3-0-0) in the matchup of Pacific Division rivals.

William Carrier and Brett Howden scored for the Knights, who return to T-Mobile Arena on Thursday to play Winnipeg. Faceoff is 7 p.m.