Napoli coach Walter Mazzarri fielded his strongest available side after being criticised for resting too many key players when losing to Chievo in midweek.
But there was no beating the team from Florence.
Indeed, the visitors had the better chances of the game and went closer to collecting the three points than their hosts.
Fiorentina looked positive in the first half with Sinisa Mihajlovic's side listening to their coach's pre-match advice not to show any fear.
They had the best chances with Riccardo Montolivo's shot on the half-hour mark testing De Sanctis, who chose the safe option of pushing the ball away as it came to him between two defenders.
Four minutes later Stevan Jovetic pulled a shot wide from the edge of the penalty area.
Even though Fiorentina were on top, Napoli had Edinson Cavani in their side and he showed how he only needs a glimpse of goal to be a threat in the 40th minute when he pulled a shot across the face of goal and wide.
It was the closest Napoli came to scoring in the first half.
Two minutes later, Gianluca Comotto almost put Fiorentina in front, but De Sanctis made a reflex save to deny him.
A mistake by Napoli defender Ignacio Fideleff almost gifted Juan Vargas with a goal five minutes into the second half, but the Fiorentina winger only found the sidenetting.
A shot over the crossbar in the 58th minute from Montolivo was the final warning for the Napoli fans, who did their best to lift their team.
The encouraged worked to a degree, with the home side enjoying a good prolonged spell of pressure, although they were unable to create any clear-cut chances.
They wanted a penalty when Manuel Pasqual blocked Juan Zuniga's cross with his hand, but the referee waved away their appeals.
Fiorentina bolstered their defence and Napoli lacked any ambition in the last 10 minutes as both sides seemed to settle for a point.