Sampdoria, who started the season with a one-point deduction, have comfortably shrugged off that deficit after recording three wins and two draws in their opening five games.
And after watching them grab an impressive point at Roma in midweek despite the early sending-off of Enzo Maresca, Napoli coach Walter Mazzarri admits his players cannot afford to look too far ahead with a tricky game coming up, despite being on a high after the 3-0 win over Lazio.
"We are only five games into the season and the road is long," he said."
We have had a great victory, and are looking at Sampdoria because it will be a tough game."
Fourth-placed Inter Milan will be without Wesley Sneijder for their Sunday clash with Fiorentina.
Sneijder pulled a muscle in his side's 2-0 midweek win at Chievo and could be out for at least two weeks. Antonio Cassano is in line to replace the Dutchman as Inter look to make it two wins in a row.
After a bright start to the season, Lazio will be desperate to shrug off two successive Serie A defeats, including their thumping midweek loss at Napoli, when they face bottom club Siena.
Catania will look to build on their midweek win over Atalanta as they travel to Bologna, while Atlanta face a Torino side who have failed to win in three after a midweek home draw with Udinese.
Udinese are at home to Genoa while the league's two remaining winless sides both have chances at home, with Cagliari facing Pescara and Palermo up against more fellow strugglers in the shape of Chievo.
On Saturday, Juventus recorded an emphatic 4-1 win over rivals Roma, while AC Milan were held to a 1-1 draw at Parma.
Sunday's Serie A Fixtures
Saturday's Serie A Results