The defender saw a speculative long ball bounce into the net after goalkeeper Morgan De Sanctis misjudged the flight of the ball and jumped well underneath it.
That goal gave Fiorentina the lead just after the half-hour mark, but Edinson Cavani levelled up just before half-time with a bullet header from Marek Hamsik's free-kick.
A bad-tempered spectacle saw six players booked, and Valon Behrami was extremely lucky not to pick up a second yellow card early in the second period.
Cavani, Gokhan Inler and Goran Pandev brought good saves from Fiorentina goalkeeper Neto, while Alberto Aquilani missed a good chance for the home side in stoppage time.
The result moves Napoli second on goal difference ahead of Lazio, but they trail leaders Juventus by five points. Fiorentina stay fifth.