Premiers Plate winners Perth Glory were beaten 1-0 at second-placed Sydney FC in the A-League.
Perth secured top spot with a 1-0 win at home to Newcastle Jets last time out but they fell to Adam La Fondre's first-half goal at Jubilee Stadium on Thursday.
Sydney move five points clear of third-placed Melbourne Victory, who are away to Adelaide United on Friday, thanks to their tight win.
Le Fondre's 16th goal of the season proved the difference between the sides as Perth were undone in the 37th minute.
The former Premier League striker was on hand to nudge home at the back post after Paulo Retre cleverly headed the ball back across goal.