A Marc Janko brace ensured the Sky Blues took all three points away from AAMI Park, where John van 't Schip's hosts struggled to break down the stubborn visitors until late in the contest.
Erik Paartalu's header and the sending off of Milos Dimitrijevic gave City hope in the closing stages, but they proved unable to snatch what would have been a dramatic equaliser.
Goals
0-1 (Marc Janko 10')
Bernie Ibini advanced down the right and swung in a deep, looping cross to the back post. Andrew Redmayne, perhaps misjudging the flight, failed to clear it and Janko got there before Patrick Kisnorbo to nod the ball home.
0-2 (Janko 83')
Wielaert's criminal attempt at a pass across his own back four gifted possession to Janko, leaving the Austrian free to waltz in on goal and slide the ball beyond Redmayne.
1-2 (Paartalu 88')
A short-corner routine saw Damien Duff float a cross into the danger zone and Paartalu's header looped beyond Vedran Janjetovic, ending the goalkeeper's streak of successive clean sheets at four matches.
Key moment
A minute after Sydney's opener Janjetovic appeared to obstruct Duff, the veteran winger going to ground inside the penalty area. Referee Kris Griffiths-Jones gave a foul against the Irishman, confounding those of a City persuasion. Had that decision gone the other way, it could have been a different game.
Opta Data key stats
City had more of the ball and registered more shots than the visitors, who demonstrated their doggedness and solidity by making 20 interceptions, 14 more than the home team.
Coach killer
Minutes after getting booked by channelling his inner Kevin Muscat, the Dutchman knocking a Sydney FC substitute off his garden chair in an attempt to retrieve the ball, Wielaert cost his team any hope of a point by serving up the ball for Janko on a silver platter.
Back to the drawing board
City had more of the ball (59.8 percent of possession) but were frequently caught on the counter in the first half, Janko hitting the post and Bernie Ibini sending in several dangerous crosses after exposing Iain Ramsay down Sydney's right.
The Sky Blues though were guilty of considerably profligacy in the opening 45 minutes, Janko and Abbas both wasting one-on-one opportunities.
If City want to play with the ball and force the issue against teams, they need to tighten up at the back and avoid being caught out.
Sydney meanwhile must be more ruthless if they are to turn their organised, hard-working foundations into consistent victories, because they won't receive gifts Wielaert's every week.
The Final Word
Sydney will visit Pirtek Stadium next weekend more confident of beating Western Sydney in their own back yard than they have since the very early days of the Wanderers' existence.
City meanwhile face a long trip to take on a Wellington Phoenix side who are likely to be out for revenge after successive narrow defeats away from home.
Teams
Melbourne City: Redmayne, Hoffman, Wielaert, Kisnorbo, Ramsay, Paartalu, Miller (Melling 46'), Mooy, Dugandzic (Marino 77'), Williams (Brown 66'), Duff.
Sydney FC: Janjetovic, Bojic, Ryall, Petkovic, Gersbach, Antonis, Abbas (Grant 68'), Dimitrijevic, Brosque, Ibini, Janko (Smeltz 94').
Scorers: Janko (10', 83'), Paartalu (88')
Red cards: Dimitrijevic (89', second yellow)
Yellow cards: Bojic (18'), Wielaert (78'), Dimitrijevic (70', 89')
Conditions: 30 degrees, dry
Attendance: 9, 474 @AAMI Park