City had been unbeaten in six league games stretching back to last season but had endured a scratchy start to the new campaign.

That came to a head on Saturday night when City were brought undone by a resolute United defence, marshalled by the brilliant Leo Lacroix and Wenzel-Halls' pinpoint finish in the 20th minute at AAMI Park.

United seized the advantage Steven Lustica pounced on a poor header from Curtis Good and nodded the ball into the path of Alessandro Diamanti.

The United captain slid a delightful ball into the path of Wenzel-Halls who took a touch then sweetly struck the ball across his body into the far bottom corner of Tom Glover's goal.

Lachie Wales had the ball in the back of the net in the 30th minute but it was chalked off for a foul.

United goalkeeper Jamie Young then denied City a near-certain equaliser in the 45th minute.

Andrew Nabbout burst down the right and whipped in a tantalising cross and while Jamie Maclaren leapt over Josh Risdon to put a header on target, Young brilliantly deflected the ball to safety with his feet.

City continued to press after half-time and in the 52nd minute Aiden O'Neill ripped a fizzing long-range strike but it clattered off the post to safety.

Three minutes later, Florin Berenguer danced along the edge of the penalty area and fed it to Nabbout who let rip with a fierce strike, forcing a brilliant diving save from Young.

From there, City huffed and puffed but couldn't blow the United defence down.

Substitute Nathaniel Atkinson forced a good save from Young with a looping header in the 82nd minute, while the United goalkeeper parried away a deflected shot shortly after.

Mathew Leckie went on a barnstorming run late but put his shot wide, summing up a fruitless night for City's star-studded attack.

Australian Associated Press