Del Piero delighted 12,691 fans at Allianz Stadium, striking the competition's second-fastest hat-trick in the first half and adding another brilliant goal after halftime.
The 38-year-old former Italy and Juventus great notched four goals in a match for the first time in his esteemed career.
"I felt free in my mind today, for sure," said Del Piero, who now has nine goals for the season.
"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 play very good from the first minute."
Del Piero had a strong supporting cast, with new signing Joel Griffiths delivering the opening goal and a fine all-round display on debut.
The performance moved Sydney to the cusp of the top six as they registered back-to-back wins for only the second time in a turbulent season.
Both Del Piero and Farina Farina hoped the performance could be a catalyst for Sydney making a run at the finals but the coach said it was imperative the Sky Blues backed it up away to Melbourne Victory next week.
"We'll enjoy tonight, but it's three points, let's be realistic," Farina said.
"Next week we go to Melbourne so unless we continue to play like that and continue to fight and work hard, it means nothing."
The defeat equalled the Phoenix's worst losing streak of four to leave them rooted to the foot of the ladder, with pressure mounting on coach Ricki Herbert.
He branded the performance "totally unacceptable."
"That's the most disappointing performance by a team that I've had at the football club," Herbert said.
Griffiths and fellow recruit Tiago were both handed starts and a fresh-faced Sydney side exploded to five-goal lead inside 39 minutes.
Former Newcastle striker Griffiths, returning to the A-League after more than four years in China, oozed class early and opened the scoring in the 11th minute when he combined brilliantly with Del Piero.
The Italian delivered a superb, lofted-through ball from almost halfway, and Griffiths read it perfectly before latching onto it from a tight angle to score.
From there, Del Piero stole the show.
He was allowed too much time and space in the box in the 21st minute when he cooly steered the ball past Mark Paston and had his brace two minutes later.
There was more than a touch of fortune as Andrew Durante was harshly adjudged to have fouled Jason Culina inside the box and Del Piero made no mistake with the penalty.
Culina scored a goal of his own in the 26th minute before Del Piero then wrapped a hat-trick inside 18 minutes, unleashing a powerful, curling shot from the top of the box.
The Phoenix were not without their chances, but headed into the sheds stunned.
There was more pain in the second half.
Del Piero grabbed his fourth in the 65th minute, tormenting Durante with some fancy footwork before unleashing another pin-point finish.
Wellington's Ben Sigmund bagged a consolation goal in the 79th minute but it could not prevent their worst ever loss.
Yairo Yau ensured that when he played a brilliant one-two with Blake Powell to score in the 84th minute, moments after Del Piero had been substituted off to an enormous ovation.
