The two clubs were keen to react to Europa League exits in midweek and the match at Stadio San Paolo offered a shot at redemption and rich rewards to both parties.
Rafael Benitez's men were itching to pull 13 points clear in the pursuit of the final Champions League place, which Fiorentina are chasing hard and could now reach over the season run-in.
Any number of players could have unlocked the frantic encounter after Faouzi Ghoulam was sent off but it fell to Spanish winger Joaquin to force the 1-0 win with a header at the death.
In the opening stages Juan Cuadrado sneaked inside the Napoli backline to test Jose Reina with a low drive.
The hosts pushed back and Gonzalo Higuain went dangerously close with a fierce effort that Neto punched clear.
The under-siege goalkeeper was soon all that stood between Marek Hamsik and the opener as he led a one-man crusade on the Fiorentina goal.
The Slovakian streaked clear to blast the ball straight down the Brazilian keeper's throat before being denied when attempting to find the top corner.
But the Tuscans' hopes of surviving the first-half onslaught received a timely fillip whenNapoli lost Ghoulam to a red card in the 38th minute.
With Fiorentina breaking forward, the Algerian left-back slid in late on Marko Bakic and received his marching orders.
Despite the setback Napoli were careful to appear in control of proceedings when play resumed and Higuain was unlucky to come up short on a fine through ball from Insigne.
And Fiorentina were determined to enjoy the extra space, Alberto Aquilani soon finding a gap that allowed him to pick Joaquin out from afar.
The Spanish winger could not fashion a chance but it was not long before Cuadrado almost surprised Reina with a shot on the volley that whistled wide.
Aquilani then warmed Reina's palms, but Jose Callejon nearly broke the deadlock with an audacious lob that Neto struggled to pluck out from under the crossbar.
The San Paolo crowd froze as Viola substitute Josip Ilicic rippled the side netting and gasped as Gokhan Inler forced Neto into yet another stop with a searing free-kick.
Insigne's poor backpass then let Gomez into the box unchecked, but Reina covered his team-mate's mistake with relative ease.
Fiorentina's last gamble appeared to be throwing striker Alessandro Matri into the fray from the bench but his introduction did not have the desired effect.
He first pinged the ball straight at Reina when well-placed to score and, in the 78th minute, improbably headed wide from a few metres out.
The match showed no sign of fizzling out to a tame conclusion and there would be a deciding moment.
Three minutes from time, Manuel Pasqual wriggled down the left to pick out Joaquin, and a straightforward header sent all three points back to Florence.