After being the top side since round nine and looking like they had their ducks in a row, the Swans were swamped in the second term on Saturday at the MCG and slumped to a 60-point hammering from the Brisbane Lions.
It follows their 81-point humiliation against Geelong two years ago.
Since John Longmire coached them to an epic grand final win over Hawthorn in 2012, Sydney have lost their last four deciders.
The Hawks reversed the result in 2014 and two years after that, the Western Bulldogs memorably broke their premiership drought two years later.
It's not quite the Colliwobbles, but whoever lost on Saturday was going to face despair given Brisbane had gone down in last year's grand final.
That it is two heavy losses in three years compounds the hurt for Sydney.
Chad Warner reacts during Sydney's big loss to the Lions. (James Ross/AAP PHOTOS)
"I don't think we gave it our best shot, compared to what we've been doing, and we didn't do what was required on the day,'" Longmire said post-match.
"I don't think we used our run enough from the start. We blasted away a bit too much.
"Then we were beaten at ground level and they were able to get it back, go back through us a bit too easy.
"We didn't put enough pressure on around the ball."
Sydney's fate was sealed when Brisbane went on a seven-goal romp in the second term, giving them a decisive lead of 46 points at the main break.
Nothing worked. Isaac Heeney, so influential in Sydney's two finals wins, finally succumbed to the stress fracture - Longmire called it a stress reaction - he had been carrying in a shin and had a bad day.
But Longmire has backed Sydney to rally, noting they have done it before after grand final heartbreak and have the resilience to do it again.
Nick Blakey and Isaac Heeney (R) watch the end of their side's heavy defeat from the bench. (Joel Carrett/AAP PHOTOS)
"It's a hard thing to do - you'd much rather get in the ring and have a swing than be standing outside, looking in," he said of making grand finals.
"Ultimately, we've been able to get ourselves in the position where we've had an opportunity and we haven't got it done today. We didn't pass the test.
"We have a group of people, right across the footy club, who are able to do that. It's very hard to win it if you're not in it."
This is also the second time, after the Bulldogs in '16, that a club has beaten Sydney for the flag after coming from outside the top four.
It will put renewed focus on the pre-finals bye, introduced in 2016. As the Lions built up a head of steam with three-straight games ahead of the grand final, Sydney had the week off after winning their qualifying final.
"I'm not going to put it down to that, but it's not the advantage it once was," Longmire said of earning the double chance by finishing in the top four.
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