Del Piero bagged a brace of almost identical counter-attacks, both launched from their own half by Cristiano Zanetti.
"We made three steps forward because we picked up three points, but it was four months back because Lazio got more shots on goal than all the other teams put together this season," moaned Juve coach Claudio Ranieri.
"We did not put in a good performance. Thank goodness we had Buffon and Del Piero tonight."
Del Piero was given a rare start due to Vincenzo Iaquinta's injury and made the most of this chance by scoring a brace.
"He had already played well last time and you can see he is in good shape, as when he starts running the defenders can't catch him. I repeat, thanks to Alex and Buffon we picked up three important points.
"Lazio put us under real pressure every time they got the ball. They showed great pride and played some excellent football. They are alive and kicking, no doubt about it."
"I already said it before the season kicked off - Inter are certainly a better team, but Juve have an indomitable spirit that I like to fire up even further. Only Inter can lose this title, but I want to be there if they do slip up."