A-League-leading Sydney FC's slump continued as they conceded sloppy set-piece goals in a 2-0 home loss to Brisbane.
Matt McKay's ninth-minute near-post header from a corner was followed 10 minutes later by Jacob Pepper's tap in after a free kick -- his first goal in six years.
Sydney's 59th-minute goal also came from a set-piece, Milos Ninkovic powering in a far-post header from a Jordy Buijs free kick.
The Sky Blues came close to salvaging a point in a frantic finish, but Brisbane held firm on Saturday night at Allianz Stadium.
Substitute Matt Simon struck a post in the 89th minute and put a stoppage-time effort into the sidenetting. Right at the death, Brandon O'Neill had a free kick tipped over the bar by goalkeeper Jamie Young.
It was Sydney's first A-League home loss in 29 games stretching back almost two years.
The Sky Blues have not won any of their past four games, and have suffered back-to-back A-League losses for the first time since April 2016.
With Newcastle winning in Wellington a couple of hours earlier, Sydney's seemingly once-unbreakable grip on the Premiers Plate has been loosened a little and their lead cut to five points with four rounds remaining.
Brisbane's fifth win in their past six away games moves the Roar above Perth into seventh, just two points behind sixth-placed Western Sydney.
Sydney looked to have pulled a goal back in the 33rd minute when defender Alex Wilkinson headed home an Adrian Mierzejewski free kick but a VAR review resulted in an offside call.
Set pieces apart, both sides were unable to create good chances in open play in the first half.
They were more successful after the break, with Sydney pouring on the pressure.
Ninkovic went close on the hour, putting a close-range shot wide and Bobo struck a 20-metre shot straight at Young in the 83rd minute.
Brisbane spent most of the second half defending, but Massimo Maccarone should have done better in the 76th minute, mis-hitting an on-target effort from close range.