Melbourne Victory closed the gap to A-League leaders Sydney with a 2-0 win away to Adelaide United on Saturday.
Kevin Muscat's side triumphed over their fierce rivals thanks to a goal in each half from James Troisi and Besart Berisha, inflicting a ninth defeat in 14 matches for the reigning champions.
Sergi Guardiola came close for the home side before Troisi fired in from Berisha's pass to put Victory ahead after 22 minutes at Coopers Stadium.
United had twice the number of shots as Victory but lacked a cutting edge and they were punished 22 minutes from time, when Troisi turned provider for Berisha to nod the ball into the bottom corner.