First-half goals from Anthony Caceres, Daniel McBreen and Matt Simon wrapped up a convincing triumph for the defending champions on home soil.
The result means Newcastle have failed to win a league fixture in Gosford since January 12, 2008, losing six matches and drawing three in that period.
Caceres set the tone after 13 minutes, unleashing an unstoppable 25-yard drive that flew past goalkeeper Mark Birighitti.
The Mariners doubled their lead after 32 minutes when McBreen seized possession on the edge of the area and arrowed a left-footed shot into the back of the net.
And the victory was complete when Matt Simon headed home Mile Sterjovski's corner in first-half stoppage time.
Ryan Griffiths' stunning last-gasp goal denied Melbourne Heart a second consecutive win as Adelaide United stole a 2-2 draw.
After Bruce Djite's 22nd-minute strike gave the Reds the early advantage, Harry Kewell coolly capitalised from the penalty spot in the 61st minute following a Nigel Boogaard's foul.
Former Leicester City and Leeds United stalwart Patrick Kisnorbo scored a superb goal 18 minutes later to give Heart the edge but Griffiths' excellent volley from Marcelo Carrusca's corner ensured the hosts had the last word.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.