Ibrahim Haydar opened the scoring for the Sky Blues with his first goal of the campaign in the 21st minuteand despite Adelaide applying plenty of pressure, Robbie Milevski doubled the advantage 13 minutes from time.
It was an apt finish for Sydney who won 13 from 18 in the regular season and ended up grabbing the first ever National Youth League title.
Goal scorer Haydar was delighted after the game.
"It was a great win. The boys had talked about it before, we couldn't lose our focus," said Haydar.
"We had led throughout the season and we knew that it would all mean nothing, we had to win."
Milevski was also on hand to share his views of the season.
"We were very confident. The boys have worked hard all year and it finally paid off for us," he said.