Rafael Benitez's men could have put the pressure on Roma – who trail champions and leaders Juventus by five points – with victory, but had to come from behind to secure a point.
Cagliari, who have lost just one of their eight Serie A home matches this season, took the lead in the ninth minute through Brazilian striker Nene.
The goal was created by Davide Astori, who centred for Nene to stroke home with his left foot.
Napoli's response was swift, though, with striker Gonzalo Higuain slotting to the left of Serbian goalkeeper Vlada Avramov from the penalty spot.
Benitez's side pressed for a winner, but were held by a solid Cagliari outfit, as both teams entered the mid-season break with one point each.
Saturday's other fixture saw Udinese win 2-1 at relegation-threatened Livorno.
Uruguay forward Nicolas Lopez pounced on a defensive mix-up to slot the opener home from a tight angle in the 11th minute.
Livorno's equaliser was an excellent goal – Luca Siligardi feigned to cut inside before thrashing past Udinese goalkeeper Zeljko Brkic 13 minutes before half-time.
But Udinese got the winner with 25 minutes to play as Thomas Heurtaux tapped in the rebound after Danilo's effort from a corner was parried by Livorno goalkeeper Francesco Bardi.
