After a cagey opening, in front of a raucous crowd at the Stadio San Paolo, Napoli almost forged a breakthrough in the 12th minute when Gonzalo Higuain's low shot was spilled by Federico Marchetti before the Lazio keeper recouped the ball.
Moments later, it was Lazio who almost took the lead as a miscued Raul Albiol clearance gave Filip Djordjevic the chance to pressure the Gli Azzurri back line before Kalidou Koulibaly managed to thwart Le Aquile.
Then Napoli wasted another chance to edge in front after a loose ball fell to midfielder David Lopez, but the Spaniard's unconvincing shot was well off target.
The Neapolitans nearly gifted their opponents the lead on the half-hour mark when Mariano Andujar botched his clearance under pressure from Djordjevic before Koulibaly again saved his team.
However, they fell behind with 12 minutes of the opening period remaining when Parolo's rocket of a shot from distance found a way past Andujar, although replays suggest that the strike took a deflection on its way into the net.
Things got worse in first-half stoppage time when a well-timed through-ball saw Candreva find space behind the Napoli back four before slotting low past the keeper.