Bobo's double and volleys to Milos Ninkovic and Adrian Mierzejewski sealed another emphatic win for the Sky Blues, humbling their third-placed opponents on their own turf.

The defeat was City's worst at home in eight seasons.

Graham Arnold's side meanwhile move ahead of their record-pulverising efforts of last season. At this stage last campaign they had 47 points but scarily for their opponents, now have 49.

Individually, their Brazilian frontman notched his 20th goal in 20 matches, putting him on pace to better Bruno Fornaroli's record 25-goal season of 2015/16.

Fornaroli, City's captain, coincidentally returned to action as a substitute after a five-month layoff in a match his club billed as the biggest of their season.

Warren Joyce's side came into the match unbeaten in six games and eager to test their form against the champions.

They were found wanting.

Man-of-the-moment Daniel Arzani's attacking runs troubled Sydney, seeing him double and tripled-teamed on the right wing, yet he got a lesson in composure from the best in the business.

Sydney streamed forward on the half-hour, when Alex Brosque lured Dean Bouzanis into taking him down into the box for a penalty.

Heartbreakingly for Bouzanis, Bobo's spot kick fizzed into the net off the crossbar after the goalkeeper got two hands to his strike.

From that moment, Sydney stepped up a gear.

The Brazilian, fresh from his 19th goal of an extraordinary campaign, laid the ball off for Mierzejewski who should have made it two.

Bobo was well thwarted by Bouzanis after Ninkovic's release and shortly after the Johnny Warren Medalist doubled Sydney's advantage.

Stefan Mauk's careless pass was well cut out by ex-City defender Michael Zullo before Ninkovic volleyed home from the top of the box.

City actually out-possessed and out-shot their opponents 14-8 but Sydney were making and taking the big chances.

Zullo, having a stormer against his old side, crossed for Bobo on 65 minutes and the Pole on 79 to complete the emphatic scoreline.

"It could have been more," Arnold said. "We missed a couple of one on ones and also one cleared off the line.

"When you have the quality of players of Ninkovic and Bobo and Adrian and Brosquey, it's dangerous if you leave space."

The result puts Sydney 12 points clear, making another premiership a mere formality.

Aside from Fornaroli's return, there was precious little for the home fans among the disappointing 8,587 crowd.

City are marooned in third place behind Newcastle after losing all three meetings with Sydney this season.

Joyce, who lost Osama Malik to a thigh injury in the warm-up, suggesting the 4-0 scoreline was barely merited.

"In the first half I thought we played some good football ... maybe we should have been goals up," he said.

Australian Associated Press