The win took them to 33 points - eight clear of defending champions Macarthur, who have three games in hand.

If the Stingrays maintain form, the top-of-the-table clash at Lynwood Park on July 19 could determine the premiership's destiny.

On Sunday, Illawarra weathered an early Manly storm before dead-ball specialist Halley Kerrigan buried a free kick from 25m out for 1-0 after 25 minutes.

Illawarra doubled their advantage 10 minutes later, when Michelle Carney finished off a counter-attacking move from deep within their own territory.

Trudy Camilleri returned after an extended injury lay-off and set up Illawarra's third goal, scored by Talitha Kramer in the 39th minute.

Illawarra maintained their advantage until half-time before Michelle Heyman completed the scoring in the 88th minute.

"The girls today took a big step in becoming a, if not the, leading side this season with a competent display; the defence was strong and also midfield showed they can stand up and play good football," stand-in coach coach Brad Cocker said.

"This was not a perfect performance, but it showed we are improving week by week and will be there when the whips start cracking."

Meantime, Christie Akid and Shelby Fenech scored in reserve grade's 2-0 win.

The under 16s lost 3-2 after leading 2-1, the under 14s scored a 1-1 draw and the under 12s lost 3-0.