Large numbers of Napoli supporters wore masks of defender Kalidou Koulibaly as their side beat Carpi 1-0 on Sunday, after the player was racially abused by Lazio fans in their previous game.
Wednesday's league match was stopped for three minutes in the second half after some Lazio fans aimed racist chants at the Senegal international.
Supporters' group Quelli del Sangue Azzurro were behind the mask appeal.
In addition, some supporters painted their faces in support of the player.
A statement read: "Everyone in Naples is offended by what happened to our young star. Because of this, we want to show our full support to Koulibaly."
Lazio were fined 50,000 euros (£38,250) and will have to close three sections of the Stadio Olimpico for their next two Serie A home games.
Napoli's victory on Sunday keeps them two points ahead of defending champions Juventus, who they play next week.