Karol Kisel's goal was enough to give Sydney FC a 1-0 victory over Melbourne Victory, ending Melbourne's finals' hopes.
The Sky Blues, in front a season high crowd of 18,180 at the newly-christened Allianz Stadium - formerly Sydney Football Stadium - produced one of their better performances of the season despite the slim winning margin.
The match immediately settled into a good tempo producing a number of half openings, the best of which saw Sydney FC goalkeeper Ivan Necevski quickly out to smother Archie Thompson who had been released by a short James Jeggo pass behind the defence.
It was to prove a false dawn for Victory and Sydney's Joel Chianese soon had an even better opening, but after evading two defenders he could not beat the advancing Ante Covic.
Midway through the half Karol Kisel latched onto a loose ball in the penalty area and his shot seemed certain to ripple the net only for Mark Milligan to appear from nowhere and make a miraculous goal-line clearance.
However, Kisel, playing in his 50th match for the Sky Blues, was not to be denied. Ubay Luzardo was adjudged to have hauled down Bruno Cazarine as a corner kick was delivered and Kisel confidently buried the resultant penalty.
It could have been even better for Kisel within five minutes, however the Slovakian fired over from near point-blank range after Brett Emerton superbly laid on the opening.
Sydney were completely dominating their opponents by the time the half-time whistle blew with only their profligacy keeping the contest alive.
The interval provided a welcome relief for the visitors and the match settled into a more even contest after the restart.
Just past the hour mark Milligan's defensive intuition again kept Victory's hopes alive with the Socceroo making another superb goal-line intervention, this time to deny Nicky Carle.
Marco Rojas and Harry Kewell flashed efforts wide as the visitors desperately attempted to revive their hopes.
Kewell, who turned in a largely subdued performance on his long-awaited return to his home city, powered a close-range header over the crossbar as Victory enjoyed a rare sight of goal.
The second half proved to be a disjointed affair and although Sydney looked the more likely to score, they were unable to convert a number of half-openings and had to make do with a one-goal margin, in the process claiming the inaugural beyondblue Cup.
The hard-fought three points leaves the Sky Blues sitting just one point out of the play-offs ahead of a visit to fifth-placed Melbourne Heart next weekend.