Mattia Zaccagni had put Lazio in front, but new buys Kim Min-jae and Kvicha Kvaratskhelia turned it around to give Napoli a previous victory away to Maurizio Sarri’s side.
The pressure was on both sides after disappointing stalemates, with Pedro not fully fit and Diego Demme injured. Luciano Spalletti shelved his changes against Lecce, returning Giacomo Raspadori and Tanguy Ndombele to the bench.
It took just over three minutes to break the deadlock, as Mattia Zaccagni was allowed too much time and space on the edge of the area to control with his back to goal, turn and drill into the bottom corner. Felipe Anderson had gone on a mazy run to set it up.
Kvicha Kvaratskhelia robbed Sergej Milinkovic-Savic and got past Patric, but the finish was smothered by Ivan Provedel.
The Georgia international did better moments later, turning Luis Alberto to unleash a screamer from distance for a strike that cannoned off the upright.
Napoli did equalise on a corner with Kim Min-jae’s glancing header that hit the inside of the post and Provedel was only able to claw it away after the ball had completely crossed the line.
On the stroke of half-time, Hirving Lozano was stretchered off after a nasty clash of heads with Adam Marusic, with fears he has fractured his cheekbone.
Matteo Politano came on and immediately surged forward, finding Kvaratskhelia with a slide-rule pass, but his first touch was a little heavy and allowed Provedel to come flying out to parry at his feet.
Napoli came out fighting for the second half with a series of chances, Provedel palming a Piotr Zielinski header off the line, then Osimhen’s flicked effort bouncing off the far post.
Kvaratskhelia blasted over from eight yards as Zielinski pulled back from the by-line, then Provedel fingertipped an Osimhen angled drive wide.
The pressure paid off and Zambo Anguissa laid off a ball for Kvaratskhelia to hammer into the net from 12 yards.
Lazio fought back, Felipe Anderson dinking it over Alex Meret only to be denied by a desperate Mario Rui interception at the near post that risked an own goal.
Moments later, Mario Rui seemed to elbow Manuel Lazzari inside the penalty area, but the referee and VAR decided not to intervene.
Meret flew to palm away a Felipe Anderson backwards header on a free kick, Mario Rui stopped Immobile nodding in a Toma Basic corner at the back post and Amir Rrahmani charged down a Pedro volley with his face.
Pedro drilled just wide of the near stick, but Napoli took the points at the Stadio Olimpico.
Lazio 1-2 Napoli
Zaccagni 4 (L), Kim Min-jae 38 (N), Kvaratskhelia 61 (N)