Perth Glory continued to sit serenely at the top of the National Soccer League playoffs as challengers Olympic Sharks and Parramatta Power battled for points.

Olympic had to turn around a 1-0 deficit on Sunday night to register a fighting 3-1 win over Adelaide City, Parramatta struggled to beat Newcastle 3-2 while Perth was untroubled in a 3-0 score over Northern Spirit.

After round six, Perth sits alone on 18 points from Olympic (13), Parramatta (11) and Adelaide City (10) with Northern Spirit (7) and Newcastle (1) trailing with four rounds left.

A spell on the sideline for Joel Porter proved just the tonic for the Olympic Sharks despite the atrocious conditions at Toyota Park.

Midfielder Porter, a Socceroo less than a year ago, has been down on form and luck of late and was relegated to the bench by coach Lee Sterrey.

His eventual appearance in the 68th minute changed the complexion of the match with the 24-year-old playing a key role in lifting his side.

In driving rain the home side looked to have again squandered a mountain of possession for no result when a Jade North clearance off the line sparked a remarkable turn of events in the 70th minute.

Olympic drove upfield on the counter before Porter laid off beautifully for fellow substitute Franco Parisi to score.

Porter then collected a through pass from Tom Pondeljak, turned masterfully in the sodden conditions and passed to Ante Milicic for the second while Parisi sealed the result in the 90th minute with his second goal.

The visitors had gone up 1-0 after 61 minutes when Pondeljak brought down City's Lucas Pantelis with Clint Bolton saving the penalty from Claudio Pelosi who then put away the rebound.

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