The Italian helped get the ball rolling in the 11th minute by playing in Joel Griffiths, who ran onto his chipped pass and finished well.
Soon after, he notched his first by receiving a Terry McFlynn cross in the box, turned his marker and sent a left-footed shot into the top corner, with his second, coming from the spot, following two minutes later.
He was involved in the goal to make it 4-0 too, releasing Ali Abbas down the left for the Iraq international to cross to Jason Culina, who finished well.
Just before the break, Del Piero completed his hat-trick, tricking the defense with a cunning drop of the shoulder and sending a cunning shot past the keeper.
His fourth and final goal arrived 20 minutes from time, and the Juventus legend left the pitch to a standing ovation from Sydney fans.