Juve had won three league games in a row before the mid-season break but produced a lacklustre display on their return to action in driving rain in Sicily.
Striker Gionatha Spinesi put Catania ahead on 15 minutes when he expertly flicked in Giuseppe Mascara's cross with the outside of his boot, although replays suggested he was just offside.
Juve coach Claudio Ranieri, a former Catania player, must have said some harsh words at halftime and his side came out with more purpose in the second period.
A goal looked beyond them, however, until Del Piero was needlessly upended just inside the box by Marco Biagianti before calmly dispatching the penalty.
Earlier second bottom Reggina drew 1-1 at fellow strugglers Empoli with Luca Saudati's fifth minute penalty for the home side cancelling out an early strike from Fabio Ceravolo.
Saudati missed a second spotkick on 16 minutes and Reggina coach Renzo Ulivieri was dismissed in the second period for protesting.
Leaders Inter Milan travel to lowly Siena on Sunday when AS Roma, seven points behind in third but on the same points as Juve, visit Atalanta.
AC Milan are expected to hand a debut to Brazilian teenager Pato in the late Sunday game with Napoli at the San Siro, where Carlo Ancelotti's men have failed to win against Italian opposition this season.