Three goals inside eight minutes late in the first half settled the issue with skipper Matt Smith, Brazilian striker Henrique and defender Jade North making it an unhappy return to Queensland for former Roar coach Frank Farina and his assistant Rado Vidosic.
The excellent Thomas Broich added the fourth late in the game with Sydney reduced to damage limitation in the second half in front of an appreciative crowd of 21,841.
To add another layer of misery for Sydney it lost main man Alessandro Del Piero to a calf injury after 30 minutes and he will be in doubt for next weekend's derby against Western Sydney Wanderers.
After stubborn resistance for 36 minutes, the wheels fell off for Sydney when Smith rose to head home a Broich free-kick through a pack of players, with Sky Blues keeper Vedran Vedran Janjetovic at fault as he scrambled at his near post.
Dire defending at a corner saw Sydney concede again two minutes later when Matt McKay's cross was headed back across the face of goal and Henrique - unmarked by any of the seven Sydney players around him - tapped home.
It was three a minute from half-time as McKay - impressing on his return to the club where he made his name - profited from a turnover from Nick Carle to feed North who finished expertly with his left foot.
The resounding win gave Roar maximum points from its first two games of the new season as highlighted it as a major title threat.
Smith was denied a ninth minute opener when his header form a corner was prodded off the line by Carle.
The home side's cause was seemingly not helped when its leading marksman Besart Berisha was forced off with a hamstring injury in the 25th minute - but Mike Mulvey's men made light of the loss as his replacement Henrique produced a stellar display.
Minutes after his departure Del Piero followed suit with Brett Emerton replacing him.
Sydney managed to stem the flow in the second half, even through Henrique had a goal disallowed and then a penalty shout waved away after he was incorrectly ruled offside.
But it couldn't last forever, and in the 79th minute Broich was well placed to ram home the fourth after a sizzling run and cross from Ivan Franjic down the right.
