But, really, the answer was simple - it all went wrong the moment Taufa Funaki absent-mindedly batted the ball out the back of the in-goal when Canterbury were threatening their first try.
Making the halfback the sole source of blame would be harsh, especially since until that point he had produced an impressive performance, setting up Salesi Rayasi's opening try with one box kick and recording a 50-22 with another.
But his miscue in the 32nd minute, which resulted in a yellow card and penalty try for making no attempt to ground the ball, was decisive.
Auckland had already once been reduced in numbers, with Blake Gibson perhaps fortunate to avoid being sent off for dropping his knee on the head of Tom Christie, who was holding onto him at a ruck.
But Funaki's absence was much more keenly felt. After the penalty try had pulled them close, Canterbury took the lead when Dominic Gardiner completed a charge-down try, taking advantage of slow ball from the ruck.
Five minutes later, Auckland's lack of halfback was further exacerbated, unable to clear from a troubled scrum. As a result, Canterbury came up with a tighthead, and Manasa Mataele soon collected an excellent wide pass from Alex Harford to score in the corner.
Harford's sideline kick made it three converted tries in 10 minutes - and left a previously dominant Auckland with a battle on their hands in the second half.
That became an even tougher battle when, without warning, Harford unleashed a 40-metre drop goal to continue an outstanding game and increase the lead to 14. And once Christie crossed for the hosts' fourth try, the fight was essentially over, ending on a sour note when Niko Jones was shown red and taken off on a stretcher after head-to-head contact with George Bridge.
Canterbury 38 (Penalty try, Dominic Gardiner, Manasa Mataele, Tom Christie, Rameka Poihipi tries; Alex Harford 4 cons, drop goal)
Auckland 20 (Salesi Rayasi, Jackson Pugh, Joel Cobb tries; Harry Plummer con, pen)
Halftime: 21-10
