The Victory also lost 5-0 away to Wellington Phoenix last time out and showed no signs of improvement on Australia Day at Etihad Stadium, as goals from Ranko Despotovic, Sebastian Ryall, Nick Carle and an Alessandro Del Piero brace, the first from the penalty spot, sealed all three points for the Sky Blues.
It was a much-needed win for Sydney FC, their first since beating Melbourne Heart 2-1 at home on December 15, and sees Frank Farina's team climb to fifth on the table, just a point behind fourth-place Victory.
The only highlight for the home side was a respectable debut for loan signing Tom Rogic, who was lively enough after coming on at half-time. Muscat's priority though is to shore up a defence which has now conceded 15 goals in the last five matches, a rate incompatible with their hopes of a top-two finish. The home side's midfield also badly missed the quality of captain Mark Milligan, who is recovering from minor knee surgery, as they slumped to their worst ever home defeat.
Those deficiencies were gladly capitalised on by Sydney, who had more of the ball in the opening exchanges and were rewarded in the 11th minute, when Terry McFlynn's well-judged long ball released Despotovic in behind the Victory defence. Nathan Coe might have come out to clear but opted not to and Nick Ansell was unable to put in a challenge, allowing the Serbian forward to run on and produce a good low finish beyond the Victory goalkeeper.
The visitors doubled their advantage eight minutes later, when Adrian Leijer put his arm around Despotovic, giving him enough of an excuse to go to ground. Referee Ben Williams pointed to the spot, and Del Piero struck a well-taken penalty into the bottom right corner.
From there, Sydney's Australia Day just got better and better. In the 24th minute right-back Ryall came in off the flank and went on a run worthy of Del Piero in his heyday, beating first Dylan Murnane and then Leigh Broxham, before toe-poking the ball past Coe and into the net to make it 3-0.
Minutes after the restart another sharp exchange of passes from the Sky Blues in and around the Victory penalty area nearly resulted in a fourth goal, with Leijer's head getting in the way of a Milos Dimitrijevic effort. Knocked unconscious and stretchered from the field after a lengthy delay, Leijer was eventually replaced by Jason Geria.
That prompted a reshuffle from Muscat, who deployed the new arrival at right-back, with Broxham dropping to centre-back and Scott Galloway moving into a holding midfield role.
The break in play cost Sydney some of their momentum, and Farina's team were content to sit on their lead and see out the half, with Victory only able to muster an Andrew Nabbout shot and subsequent half-hearted penalty appeal for handball in reply.
Carle replaced the injured McFlynn at half-time for Sydney, while Nabbout was withdrawn in favour of Rogic as Muscat sought a response from his players.
But after an improved start to the second half Victory managed to gift another goal to the visitors. In the 54th minute Nathan Coe sent a routine clearance directly to Despotovic, who played Del Piero clean through for the easiest of finishes.
Sydney grabbed a fifth with three minutes to go, Galloway giving the ball away to Carle on the edge of the area before the substitute finished smartly, sending the Sky Blues into next Friday's game away to Melbourne Heart on a considerable high.
Victory meanwhile, who were disjointed during their rare forays forward late in the second half, must make the long trip to face Perth Glory away on the same night rocked by successive thrashings.
Melbourne Victory 0
Sydney FC 5 (Despotovic 11', Del Piero 20' (p), 54', Ryall 24', Carle 87')
24,354 @ Etihad Stadium
