Lazio looked much sharper than in the final stages of last season, when the combination of a crowded fixture list and a spate of injuries wrecked their title challenge as they finished fourth.
They were given a helping hand by the Cagliari defence, which went to sleep in the fourth minute and allowed Lazzari to tap in undisturbed from point-blank range after Adam Marusic got away down the left and crossed.
Lazio were a constant threat on the break after that, although their final pass was often poor, as was their finishing.
But they finally added a second in the 74th. The ball was played out of defence to Marusic on the halfway line, and the Montenegrin flicked it over his marker, burst down the left and laid the ball off to Immobile who side-footed past goalkeeper Alessio Cragno.
It began disastrously for the visitors as a defensive mistake led to veteran Fabio Quagliarella opening the scoring for Samp after eight minutes, making him the club's joint third all-time leading scorer alongside Gianluca Vialli.
Caldirola then headed Benevento level in the 72nd minute, and Gaetano Letizia completed a dramatic fightback two minutes from time with a low shot from outside the area.