The Biancocelesti wobbled and lost at home to Atalanta last time out but made amends at the Stadio Sant'Elia as goals from Senad Lulic and Keita Balde Diao lifted them above Hellas Verona and towards the Europa League spots.
Cagliari, who had recently stabilised themselves in mid-table by producing a three-match unbeaten run, had the chance to level when one goal down in the second half but Mauricio Pinilla missed his penalty.
To compound their disappointing afternoon, Daniele Conti was dismissed for earning a second yellow card late on.
Lucas Biglia and Lulic took tentative shots in the opening stages as Lazio gauged the strength of their hosts' defence.
It would be the Sardinians who first found the target, however, with Andrea Cossu forcing a smart save from Federico Marchetti.
Lazio survived that sticky moment and punished Cagliari for missing the chance as Lulic streaked upfield to seize on Alejandro Gonzalez's pass and turn the ball beyond Vlada Avramov in the 19th minute.
Gonzalez then went close himself. The Argentinian found himself all alone in the Cagliari box but sent his header wide of the mark.
Victor Ibarbo gave home fans some reason to be hopeful before the break as his angled effort sent Marchetti scrambling across his line to punch clear.
The game opened up once more around the hour mark, and Miroslav Klose was desperately unlucky not to score after tricking his way into the box before letting rip with his left foot.
In the 68th minute Cagliari were presented with a gilt-edged opportunity to level, but Pinilla missed from the spot after Gonzalez had fouled Matias Vecino to concede a penalty.
And just as the islanders had been punished for their wastefulness in the first half, Lazio pounced while their opponents were down in the dumps again to pull two goals ahead through Keita.
Only a minute after the penalty miss, Lazio's Spanish striker picked up a slide-rule pass from Klose to clip home.
The task was beyond Cagliari from that point on but their cause was certainly not helped by Conti, who earned himself a second yellow card and a red in the 77th minute for leading with his elbow in a aerial challenge with Biglia.