The clash was Ufuk Talay's first in charge of Sydney since replacing Steve Corica during the week and the Sky Blues turned on the style for their new coach.
"I just wanted a good performance and I always believe that if we focus on the performance then eight or nine times out of ten we get a good result," Talay said.
"So that's something we definitely did and at the same time they rewarded themselves with the opportunities they created."
Joe Lolley starred with two goals and two assists while young midfielder Jaiden Kurchaski also notched up a brace and an assist.
Sydney made the perfect start when Lolley broke the deadlock after just four minutes.
Kucharski released the English midfielder out wide on the right, before he cut inside and picked out the top corner with a powerful left-foot drive from just inside the area.
Lolley had a brace on 13 minutes when he found himself in the right spot at the perfect time.
A near-post corner from Robert Mak became a scramble inside the area which was helped on by Joel King. It found Lolley who was unmarked at the back post and tucked the ball away from close range.
The visitors made it three on 31 minutes when Kucharski grabbed his first A-League goal.
Fabio took possession and laid off for the young midfielder who charged forward before sliding under Reds' keeper Joe Gauci from eight metres.
A minute before half time Lolley and Kucharski combined for Sydney's fourth to complete the first-half demolition.
Lolley drove through the Reds' defence and slipped through Kurcharski who dinked it over the onrushing Gauci.
Adelaide coach Carl Veart made a triple change at the break in the hope of resurrecting the Reds but a minute into the second half Sydney scored a fifth.
Lolley was involved again after his side won back possession in midfield, lifting an expertly weighted cross into the area for Fabio who was perfectly positioned between two defenders to nod home from six yards.
The visitors would have added a sixth on the hour if not for the heroics of Gauci.
Fabio was slipped through by Anthony Cacares and squared across the face of goal for Mak but his shot was brilliantly kept out by a diving save.
United pulled one back in the 67th minute when Zach Clough converted a spot kick after he was bundled over inside the area by Mak.
Reds coach Carl Veart was blunt in his assessment of United's performance.
"We knew Sydney were going to come out hard in the first 15, 20 minutes," he said.
"And we just didn't deal with it. We were second to everything and very naive in the way we played."
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