The win’ was the Jets’ biggest over their arch enemy, eclipsing the 5-1 rout at the same venue in round one.
They become just the second team to score eight goals in A-League history.
The Jets finish the regular season on 50 points, the club’s best ever return, and have scored an incredible 57 goals.
However, the victory did come at a cost with Ben Kantarovski (hamstring) limping off just before half-time and is in doubt for the grand-final qualifier at home in a fortnight.
Wellington’s upset 2-1 win over Melbourne City in the earlier game on Saturday moved the Phoenix to 21 points and above the Mariners.
It is the second time in three seasons Central Coast have collected the wooden spoon and a bitterly disappointing way for club great Josh Rose to end his career.
The Jets travelled down the F3 having not scored in three hours; after 25 minutes in Gosford, they had three in the bank.
Coach Ernie Merrick brought Champness into the team and pushed Jason Hoffman forward to give the attack pace and a threat in behind.
Daniel Georgievski found McGree on the edge of the box and he slipped a beautiful pass for Champness. The rookie took a touch and stroked a low shot past Ben Kennedy for his fifth goal of the campaign.
O’Donovan doubled the visitor’s advantage in the 20th minute, running on to a slide-rule pass from Steve Ugarkovic and directing the ball past a helpless Kennedy.
The goal was the Irishman’s eighth of the season but first since round five.
McGree was next, curling a low shot through traffic and past Kennedy for 3-0 after 24 minutes.