Sydney FC only needed a point to clinch the Premiers' Plate but Newcastle Jets came from behind to beat them in their own backyard.
In their first game since Robbie Fowler left the club, Brisbane Roar fell to a 1-0 loss to Adelaide United, who were also under a new coach.
Australia's loss is Macarthur FC's gain with Ante Milicic to honour his three-year contract.
Perth Glory edged a tight contest with Central Coast Mariners on their return to A-League action with Dane Ingham the match-winner.
Sydney FC left it late but got the win over Wellington Phoenix, meaning they have one hand on the Premiers' Plate.
Melbourne City confirmed veteran Spaniard Markel Susaeta mutually agreed to terminate his contract due to family reasons.
After replacing former Liverpool defender Markus Babbel in January, Jean-Paul de Marigny has been rewarded with the permanent role.
Alessandro Diamanti, 37, has extended his contract with Australian side Western United.
The 2019-20 A-League season has some clarity following Wednesday's announcement.
Brisbane Roar announced Robbie Fowler would not be returning to the club as head coach.