All five goals were scored in the opening period, with Del Piero's 37th-minute penalty the decisive moment.
Sydney had to cling to their lead, however, after Marc Warren was dismissed on 25 minutes.
The hosts raced into a 2-0 lead thanks to goals from Richard Garcia (3) and Sebastian Ryall (15), but Victory were level 12 minutes later through Archie Thompson and James Troisi.
Warren saw red in amongst the Victory comeback, but Del Piero's penalty stopped the away side's momentum before Sydney hung on for their second win after half-time.
Newcastle Jets claimed their first win of the season with a 2-1 result at Adelaide United.
Defender Kew Jaliens scrambled home to only goal of a first half dominated by the Jets, who got further reward on 52 minutes when Adam Taggart expertly chipped over the onrushing Eugene Galekovic.
Fabio Ferreira gave United a lifeline on 71 minutes but their hopes ended with Nigel Boogaard's dismissal in injury-time.
Wellington Phoenix remained winless after they failed to capitalise on Andrew Durante's fourth-minute opener to draw 1-1 with Perth Glory.
Ryo Nagai equalised for Glory on 29 minutes against a Phoenix side without a host of New Zealand internationals as they prepare for their World Cup play-off against Mexico.