PERTH Glory clinched the Premiers' Plate and officially ended Newcastle's finals hopes with a 1-0 victory at HBF Stadium on Sunday night.
Newcastle needed nothing less than a victory to stay in mathematical contention for the play-offs, but the loss leaves them eight points behind the top six, with just two games to play.
Perth's goal came in the 65th minute from Ivan Franjic after a pinpoint through ball from their Spanish veteran, Diego Castro.
Franjic placed the ball under the desperate dive of Glen Moss for his second goal of the season.
The win lifted Perth to 57 points, eight clear of second-placed Sydney, and assured them of home-ground advantage should they qualify for the grand final, as well as a berth in the Asian Champions League next season.
Both teams earlier had goals disallowed for offside.
Newcastle's Roy O'Donovan looked to have scored his 10th goal of the campaign in the 14th minute but was denied by the Video Assistant Referee.
Joel Chianese headed home from close range in the 58th minute but earned the linesman's flag.
Newcastle threw everything at Perth in the dying exchanges but the home team held on for their 17th victory in 25 games this season.
The Jets now have two games remaining, against Brisbane (away) and Sydney (home), that are effectively dead rubbers.