Lazio brought an end to Napoli's eight-match winning streak in Serie A with a surprise 1-0 victory at the Stadio Diego Armando Maradona.
Matias Vecino struck the only goal of the game in the second half with a thunderous effort from distance in a frustrating game for the hosts.
Solid defending from Lazio thwarted I Partenopei, who were largely limited to efforts from distance and struggled to break down the visitors.
Late chances did come Napoli's way though, Victor Osimhen hitting the bar and Kim Min-Jae's rebound brilliantly saved by Ivan Provedel as Lazio head coach Maurizio Sarri inflicted only a second league defeat of the season upon his former team.
Lazio almost stunned the home fans inside five minutes, Vecino flicking a header from Mattia Zaccagni's free-kick towards the far corner but Giovanni Di Lorenzo was on hand to make a crucial goal-line clearance.
First-half opportunities were limited for the hosts, Andre-Frank Zambo Anguissa having the first sight of goal with a drilled effort from distance that deflected off Sergej Milinkovic-Savic and whistled just over the bar.
Napoli's inability to threaten Provedel's goal continued after the break, Khvicha Kvaratskhelia spurning a free-kick in a dangerous position by firing harmlessly into the stands, before Piotr Zielinski dragged wide from just outside the box.
The deadlock was finally broken by the visitors after 66 minutes, Vecino unleashing a thunderbolt into the right-hand corner of the net to leave Alex Meret helpless.
Napoli came agonisingly close to an equaliser 11 minutes from the end, Osimhen heading against the crossbar and Min-Jae immediately seeing his own effort clawed off the line by Provedel.
Milinkovic-Savic came close to consolidating Lazio's win after striking the frame of the goal with a late free-kick, though it mattered little as the visitors held on for a important win in their hunt for Champions League qualification.