In stumbling 1-2 at Perth, Central Coast had their lead trimmed to a point by the Wanderers who beat Melbourne Victory 2-1 away.
With the Victory now six points out of the lead with six to play, the March 2 clash at Gosford between Central Coast and Western Sydney is a potential minor premiership decider.
Graham Arnold, last season's coach of the year and at the Central Coast club since the start of the 2010-11 season, tagged the loss at nib Stadium as "the worst performance in my time at the Mariners".
That Shane Smeltz returned to goalscoring form would not have helped Arnold's humour.
Melbourne Victory, one of three teams to lose 1-2 on Saturday, face the Mariners in the late game on Saturday, the match of the round.
The Phoenix meet Adelaide in Sunday's early game, having lost 1-3 to that side twice this season.
Sydney FC travel to Melbourne Heart in the last game of the 22nd round.