The Warriors have had some inexplicable performances over the years, but this one will be near the top of the tree.
In terms of scars, the physiological effect of this defeat might take a while to shake.
It wasn't just a bad day at the office - this was the Warriors' worst collapse in their history - as they gave up a 22-point halftime lead to lose 36-28 to the Panthers.
On three previous occasions the Auckland team had forfeited an 18-point advantage to lose, including twice in the 2012 season, but this was a new low.
It's the kind of loss that will prompt special midweek meetings, and lead to speculation that the old demons have re-emerged at Mt Smart.
"It's bitterly disappointing," said prop Jacob Lillyman. "We gave them that game. We have got to have a good hard look at ourselves and regroup during the week."
The Warriors held a 28-6 advantage at the break, after a spectacular first half that yielded five tries. But that was as good as it got. They came out in the second half looking as if they just needed to coast to the finish line, with an attitude that the match was already won. That was never going to happen; not against a Penrith side that have endured so many setbacks this year and were desperate.
In hindsight, it's no wonder the Panthers reneged on their deal to play the Warriors in Christchurch this year. Penrith were once known as the "Chocolate Soldiers", but it's the Warriors who tend to melt when they travel to the foot of the blue mountains.
They haven't won there in five years, including a limp 2014 defeat which blew a golden chance to make the playoffs. The nadir came under Matt Elliott in 2013 with the infamous 62-6 humiliation, but given the context this defeat was probably worse.
The most concerning aspect of the second half fade was the inability to arrest Penrith's momentum; it was like watching someone trying to stop a tsunami with a beach umbrella. Penrith are a good side - who have under-performed this year - but they are not that good.
But none of the senior Warriors men in the second half stood up. Not Kieran Foran, who was superb in the first half, but faded after halftime. Not Ryan Hoffman, nor Roger Tuivasa-Sheck, who had an uncomfortable day at the back. Not Isaac Luke, not Ben Matulino and not Shaun Johnson, who was successfully targeted by the Penrith attack. This performance again magnified the importance of Simon Mannering, as it is hard to imagine a similar second half collapse with him on the field.
After the hard won gains of the last month - with the 14-13 victory over the Roosters and admirable performances in Canberra and Melbourne - it feels like the Warriors are back to their uncertain selves. Every other side in the NRL will know that the Warriors are still susceptible to the shakes, still able to beat themselves if the opposition can stay in the contest.
This wasn't how it was supposed to be in 2017, and such a result probably doesn't help their ongoing recruitment efforts.
The turnaround is baffling, even in hindsight. When David Fusitu'a ran 90 metres to score on halftime, the result looked beyond doubt.
But the Warriors were lethargic from the start of the second half, while Penrith were all purpose and determination. Two quick Panthers tries seemed to drain the resolve from the Warriors, and it was one-way traffic after that.
Warriors 28 (K Foran, C Nicoll-Klokstad 2, R Hoffman, D Fusitu'a tries; S Johnson 4 goals)
Penrith 36 (I Yeo 2, D Watene-Zelezniak, W Blake, M Moylan, T Peachey tries; N Cleary 6 goals).