The Flames had won four straight and had points in six games, suddenly surging and playing like the team most fans expected this season.
The way they expected this season.
The Avalanche, meanwhile, were considered by some pundits as the best team in the league right now heading into the tilt, winners of six straight.
They were second in the Western Conference at 19-8-2, and were 8-2 in their last 10 outings.
So, Monday was a litmus test.
Folks wanted to see just how far this Flames team had come.
They answered that emphatically.
They battled back from 1-0 and 2-1 deficits to win a thriller 5-4 in overtime.
Sean Monahan had the dagger in extra time, Derek Ryan, Matthew Tkachuk, Andrew Mangiapane and Michael Frolik also scoring, while David Rittich was a beast between the pipes - yet again - making 28 saves.
Just 35 seconds into the tilt, Rittich was tested by Mikko Rantanen, who found himself at the right place, at the right time to grab a rolling puck in the slot, but wasn't able to get off a perfect shot due to the bobbling biscuit, still the Flames 'tender having to make an important stop.
Ryan Graves opened the scoring at the 4:32 mark of the first on a play that started with a great stretch pass from defenceman Samuel Girard up to J.T. Compher, to Joonas Donskoi, to Graves for the finish, his shot finding a hole under Rittich's arm.
The shots ended up 10-9 Calgary after 20 minutes, both teams with quality chances above and beyond the lone goal.
Rittich made two huge stops in quick succession on Rantanen and Avs captain Gabriel Landeskog off a rush, while the Flames best chance was courtesy of the familiar duo of No. 13 and No. 23, Johny Gaudreau making a pass back in the slot to a trailing Monahan but Colorado goalie Pavel Francouz was able to slide and make the stop.
Oliver Kylington was whistled for the only penalty of the frame - a tripping call - but Calgary's top-end PK stood tall.
Early in the second, Rittich came up big again against Rantanen - who had beat Noah Hanifin wide and cut hard to the net - by kicking out his right pad to deny the shot.
Later, Gaudreau wired a shot from a sharp angle which Francouz looked like he thought beat him, but the puck ended up under his back as he was laid out in the crease.
Ryan's tally at 9:33 tied it up, albeit briefly.
He deftly tipped a point shot from Kylington that beat a screened Francouz - who had Lucic parked in front of him battling for position, the puck past him and bouncing back out of the net before he heard the whistle.
Tweet from @NHLFlames: Don't forget to tip. #CGYvsCOL | #Flames pic.twitter.com/rHJiGQWAxq
But a scant 31 seconds later, the homeside took the lead again, Valeri Nichushkin gathering up the rebound from a Graves shot and taking a few strides and wrapping it around the outstretched leg of Rittich.
After killing another powerplay - captain Mark Giordano called for a slash as he chased down Nathan MacKinnon on a breakaway, the Avs star shooting wide - the Flames got a powerplay of their own after Gaudreau was held by defenceman Mark Barberio.
Elias Lindholm won the faceoff, the puck going up to Giordano up at the point, who feed Matthew Tkachuk on the sideboards, Chucky taking a few strides and snapping a deadly wrister that beat Francouz short-side - who was screened by Lindholm.
Tweet from @NHLFlames: ������ TARGET ACQUIRED ������#CGYvsCOL | #Flames pic.twitter.com/2P2GCHHQtn
The fans at the Pepsi Centre still hadn't settled back into their seats after the second intermission before Mangiapane made it a 3-2 game just 12 seconds in, beating Francouz high far-side after pressure forced a turnover in the Colorado zone.
Mangiapane came out of the corner, made a short pass to Tkachuk in the slot who passed right back and he snapped it home.
Tweet from @NHLFlames: A look back at the goal that got this craziness started. Skate ������ stick ������ shelf.#CGYvsCOL | #Flames pic.twitter.com/yB7fcJGHRS
The crowd was further stunned 1:27 later when Tobias Rieder feed Frolik for a tap in off a rush.
Rieder's hand-eye - then foot-eye - was simply ridiculous. Words don't do it justice, so just watch it below.