Young Socceroo Matthew Osman has struck a mighty blow for the Central Coast's A-League survival, scoring the winner in the Mariners' 1-0 victory over Newcastle in the opening leg of their minor semi-final.

Osman's diving header in the 74th minute ensured the Jets paid dearly for their inability to hit the target on home soil after holding the upper hand for much of the all-NSW clash at EnergyAustralia Stadium.

The Mariners now need only a draw at next Friday's second leg at Central Coast Stadium to progress to the preliminary final, while the Jets' title hopes hang by a thread in the cut-throat semi-final.

After a pair of disappointing losses to end the regular season, Newcastle returned to form in front of a vocal 10,236-strong home crowd.

But a bunch of missed chances, notably from Matthew Thompson and Paul Kohler in the first half, meant all the home side's good work came undone in the final 20 minutes.

Mariners winger Wayne O'Sullivan had proved a handful all game for the Jets, and again found space down the right flank to fire a cross in for Noel Spencer in the 74th.

The Central Coast skipper's powerful header was brilliantly saved by the right hand of Jets 'keeper Liam Reddy, but the rebound fell perfectly for Osman who pounced to claim the spoils.

It was an unfortunate goal for Reddy, who despite one mistake early in the first half, was superb for the Jets.

He saved his team from travelling to Gosford with two-goal deficit after another remarkable save from a close-range O'Sullivan header in the 90th minute.

The result extends the Mariners' unbeaten streak to 10 games, while serving the Jets their third straight defeat, all at home.

Adelaide and Sydney play in the first leg of the major semi-final at Hindmarsh Stadium on Sunday.

The winner of that series goes straight to the grand final, while the loser plays the winner of the Jets and Mariners in the preliminary final.

Mariners coach Lawrie McKinna revealed he had planned to replace Osman just moments before the goal.

"He was struggling ... and we just spoke two or three minutes before about him coming off," McKinna said.

"We told him to give us another few minutes so we could get the sub ready, and he's popped up in the six yard box to get a rebound and get his head in there.

"So credit to him to at least make the effort to get there. He could have easily sat back at the halfway line, but he did the hard yards and got the goal that he deserved."

McKinna said he would have been happy with a draw, but was expecting the Jets to come out firing in the return leg.

Newcastle coach Richard Money was only looking for positives after the match, and boldly declared the tie was not over.

"I thought it was a positive performance, I thought we played well, and I think we gave a performance many people didn't think we could give," he said.

"I thought the crowd had gone away happy. I thought it was an excellent cup tie, an excellent derby. I could not have asked any more of the players. We just need a break.

"As long as we keep creating chances I'm quite happy ... we'll go down to Gosford full of confidence."This tie is not over. Anyone who thinks it is, is kidding themselves."

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