Brisbane's win confirms the Sky Blues' first silverware in seven years as the runaway leaders enter Sunday's clash with Perth 11 points ahead of the second-placed Victory with three rounds to play.
But Maclaren's 51st-minute super strike at Suncorp Stadium proved just as important for the Roar as it sealed their finals position, solidified fourth spot and provided relief from some late-season wobbles.
The discarded Socceroos striker outsmarted defenders Alan Baro and Nic Ansell to latch on to a speculative long ball by Avram Papadopoulos before lobbing Victory goalkeeper Lawrence Thomas from 25 metres.
It was his sixth goal in seven matches at a time Postecoglou is looking for more from his finishers in a stuttering 2018 FIFA World Cup campaign.
Former Roar defender Jason Geria had a gilt-edged chance to equalise with 20 minutes left but failed to deliver for the understrength Victory.
With Luke DeVere making his return from a month-long calf injury as skipper, the Roar had been the dominant team for most of the night.
The scoreless opening half featured two booming long-range strikes from Brett Holman and Jack Hingert, both of which went inches from putting the home side ahead.
Only the left upright denied Holman from a repeat of his 2010 World Cup goal against Serbia while Thomas produced a superb leaping save to tip Hingert's longer effort over the bar.
Missing four internationals including Besart Berisha and James Troisi, the gallant visitors still showed some bright signs, especially with Mitch Austin threatening on the left edge before copping an blow to his ankle.
