The Sky Blues spurned the chance to go nine points clear at the top of the table on Saturday night at Allianz Stadium, in a performance as anaemic as the scoreline.
They equalled their record nine-game undefeated streak of 2006-07 but were fortunate, given last-placed United played with a confidence that belied their winless season, in a sign a victory is close.
Suspended coach Guillermo Amor needn't have worried how his defending champions would fare without him on the sidelines, as the Reds attacked with venom in and end-to-end start barely resembling its top-versus-bottom billing.
Ryan Kitto found joy on the left flank as he and Ben Garrucio targeted the in-form Rhyan Grant.
But the frenetic opening exchanges soon dissolved into scrappy play rife with turnovers that yielded few chances for either side.
Isaias and an under-performing David Carney went into the book while tough defender Matt Jurman suffered a horrible head clash during an aerial challenge with James Holland that left him bleeding heavily.
A bandaged Jurman eventually returned and earned enthusiastic cheers from the 13,179 crowd for each of his three headers in quick succession.
That was the main first-half entertainment apart from a sole opportunity apiece.
The first belonged to Adelaide defender Tarek Elrich, who fired off a 20-metre left-footed strike that shaved the outside of the post.
Soon after, a quiet Filip Holosko burst into space but, under pressure from Iacopo La Rocca, applied too much angle on his finish.
In the second half, Sydney coach Graham Arnold sensed the need for change and replaced Holosko with skipper Alex Brosque and eventually Bobo with Matt Simon, while Henrique returned for Adelaide at the expense of a cramping Nikola Mileusnic.
Holland came closest after the break, skipping past three Sydney defenders only to botch his finish, while Simon sent one wide and Alex Wilkinson took a feeble stab that was indicative of a squad perhaps more focused on next week's FFA Cup final.
