Del Piero put the Sky Blues in front in the 43rd minute after he weaved past two defenders to deliver a superb opener, while Serbian striker Ranko Despotovic struck just three minutes later to put Sydney in command.
Maltese international Michael Mifsud gave Heart hope with a goal in the 72nd minute but the visitors couldn't find the equaliser.
Brisbane Roar lead the competition by five points after ten rounds following a 2-1 win over Wellington Phoenix in New Zealand. Matt Smith and Ivan Franjic scored for Roar while Costa Rican Carlos Hernandez netted his first goal for Phoenix with a second-half penalty.
Western Sydney Wanderers are second after ending their winless run with a 1-0 victory over Newcastle Jets. The Wanderers had not won for three weeks, but striker Mark Bridge netted the only goal in the 33rd minute to ensure victory.
Adelaide registered only their second win in ten matches under Spanish coach Josep Gombau with a 4-0 hammering of defending champions Central Coast Mariners in Adelaide.