At 5:51 of the first period in the Canucks/Flames game, Vancouver requested a Coach's Challenge to review whether Calgary was off-side prior to Sean Monahan's goal.
After reviewing all available replays and consulting with the Linesman, NHL Hockey Operations staff determined that Calgary's Micheal Ferland was off-side prior to the goal. According to Rule 78.7, "The standard for overturning the call in the event of a 'GOAL' call on the ice is that the Toronto Video Room, after reviewing any and all available replays and consulting with the Linesman, determines that one or more Players on the attacking team preceded the puck into the attacking zone prior to the goal being scored and that, as a result, the play should have been stopped for an "Off-side" infraction; where this standard is met, the goal will be disallowed."
Therefore the original call is overturned - no goal Calgary Flames.
The clock is re-set to show 14:13 (5:47 elapsed time), when the off-side infraction occurred.