The former Juventus and Italy forward was recently recruited by the A-League outfit, becoming the biggest name to play in the Australian game.
Del Piero, who turns 38 in December, was praised for showing intermittent "fabulous quality" in Saturday's match by manager Ian Crook, but the Italian knows he must sharpen up.
He said: "I played 90 minutes but I need to do better. I need to improve physically and (playing) with the team and I have to do it soon.
"I'm not satisfied because we lost. But it's the first match. We need to improve. We need to play together a few times because I've only been here a few weeks and we've played just one game together."
Crook said of the star signing's performance: "I didn't think he was too bad I think he showed at times some fabulous quality for someone who got off the flight two weeks ago.
"At times I thought some of the stuff was fantastic. But we were expecting that anyway because he is who he is and what he is, which is a top-class pro."