Lazio is currently having one of the worst defensive performances of its ongoing Serie A campaign.
Napoli has so far notched four goals, including one coming from a top-class finish from Dries Mertens.
In the second half of the match, Mertens latched off a one-time finish that Pepe Reina simply had no chance of saving.
Napoli has essentially clinched all three points from this fixture and will now be five points above Lazio in the league standings, although the Biancocelesti do have a game in hand.