Milan, who had drawn four of their previous five league matches, moved up two places to fourth on 61 points, one ahead of fifth-placed Inter Milan and three more than Atalanta in sixth who both have a game in hand.
Pioli suffered an early setback when forward Rafael Leao suffered what looked like a muscle injury and had to be substituted by Alexis Saelemaekers in the 11th minute.
Last season’s champions took the lead in the 17th minute after Olivier Giroud took advantage of a Lazio defensive error to set up Bennacer inside the box for the midfielder to bundle the ball past goalkeeper Ivan Provedel.
Hernandez delighted the San Siro crowd when he lobbed Provedel with a superb shot from distance to double the lead for Milan just before the half-hour mark.
The Frenchman sped through the entire pitch to finish off an impressive solo effort, which started right outside Milan’s own box.
Disciplined Milan continued to dominate a slow Lazio side after the break and halftime substitute Malick Thiaw could have made it 3-0 after connecting with a corner, however, his header went narrowly over the bar.
Milan winger Ante Rebic had another good chance but his low strike was disallowed for offside.
Maurizio Sarri’s men showed more intent late in the game, and Luca Pellegrini was close to pulling a goal back but could only find the side-netting with his close-range shot.
Powerless Lazio, who suffered their third loss in four Serie A games, ended the clash with no shot on target.
They stayed second in the standings and have a one-point advantage over Juventus, who travel to Atalanta on Sunday.
Milan, who on Wednesday host Inter Milan in their first Champions League semifinal since they won the trophy in 2006-07, will next face Spezia in their bid to take another step towards securing a top-four spot.
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