The 38-year-old former Juventus stalwart was involved in six goals before he was substituted after thoroughly entertaining more than 12,500 fans at the Allianz Stadium.
"I felt free in my mind today, for sure," Del Piero said after helping his team to jump to sixth place in the 10-team league with their biggest A-League triumph.
"It's a day from the heavens because when you score four, for sure it's a great day.
"I'm really happy, not only for the four goals but because we played very good from the first minute."
New signing Joel Griffiths latched on to a Del Piero lob to open the account in the 11th minute before the former Italy great himself made it on to the scoresheet.
His back to the goal, Del Piero received a low cross and swivelled to bury the ball into the top left corner. He got his second within a minute, converting from the penalty spot after Jason Culina was brought down inside the box.
In no mood to relax, Del Piero released Ali Abbas down the flank before the ball reached Culina who slotted home in the 25th minute.
Del Piero completed his hat-trick with a powerful, curling shot from the top of the box as Sydney went into the break with a 5-0 lead.
Del Piero scored his fourth goal in the 70th minute before going off the pitch to a standing ovation.
Ben Sigmund scored a consolation goal for the visitors before Yairo Yao struck to complete the rout.