Marking his A-League debut in style, Tilio, 18, was thrown into the contest late in the match at Gosford but it took just over a minute for him to score of Van Der Saag's assist.

Van Der Saag, who has played seven A-League games this season, scored just two minutes later to secure victory.

"You've got to believe in these young boys and give them the opportunity and they're starting to get the opportunity now," coach Steve Corica said after the 3-0 win.

"They are our depth in our squad. They are putting pressure on the older boys in the squad.

"I think to come on and do that in a game where we really needed them to stand up and to be brave and they did. They did a wonderful job."

The ladder-leaders were under pressure from the Mariners but held on to score their sixth straight win with the injection of energy from the young guns.

Both played in Sydney's 4-0 Asian Champions League loss to Yokohama F Marinos in Japan, but Sunday's match in particular was special for Tilio.

"He's been waiting a long time. He's been looking really good at training, really strong," Corica said.

"You can see he got a chance in Yokohama and I saw something I really liked.

"He's got an ability to run with the ball and take pressure off us and in the Youth League he's been banging in goals.

"We needed him to score today and I'm very pleased for him, and Harry as well.

"They work extremely hard, they're getting stronger all the time and their fitness is getting better and you can see that. I'm just happy for them."