Sydney FC capitulated to a stunning 5-2 defeat against Adelaide United on Sunday allowing Canberra United to snatch the W-League premiership on the final day of the regular season.
It is Canberra's second premiership in the past three seasons.
Needing a win for their third top-of-the-table finish, Sydney FC somehow conspired to concede four goals in the opening 23 minutes of a chaotic second half against second-from-bottom Adelaide.
Canberra United defeated Melbourne Victory 5-1 on Saturday to lock up a home semifinal and heap the pressure on the Sky Blues for their visit to Adelaide.
Sydney FC had previously won 12 straight against Adelaide, yet showed of their normal attacking fluency when it mattered most.
Instead it was Adelaide who had the better of the first half, before finally turning the pressure into goals by scoring twice inside the opening three minutes of the second period.
An own goal from Servet Uzunlar and the first of a second-half double from Adriana Jones saw Adelaide race to a two-goal advantage within minutes of the restart.
What a 2nd half! 🙌 Awesome way to end the season!
Thanks girls for your efforts in 2016/17.#AUFC #ForeverUnited pic.twitter.com/WGavMtZ7XG
— AUFC Women (@AUFCWomen) January 29, 2017
To their credit, Sydney FC drew level by the hour mark with a quickfire double from halftime substitute Remy Siemsen, though her second was tapped home from an offside position.
However, the in-form Adelaide always looked dangerous and they soon regained the lead via a Jones penalty and an Emily Hodgson strike, before Sofia Huerta iced the cake late on.
The day got even worse for Sydney FC as Perth Glory edged a last-minute 1-0 victory over Western Sydney Wanderers to leapfrog into second.
That lone injury-time strike from Caitlin Doeglas ensured Perth Glory earned home advantage for next week's semifinal against Sydney FC.
Melbourne City will travel to Canberra United for the other semi, with the champions sneaking into fourth spot courtesy of a 2-0 win over Newcastle Jets in Coffs Harbour on Friday.