The Campanian club were cast adrift in the race for the Scudetto when the Italian Football Federation meted out a two-point deduction for the illicit actions of a former player.
Matteo Gianello had attempted to fix a match in 2010, with defenders Paolo Cannavaro and Gianluca Grava given six-month bans for allegedly failing to report his activities.
But Napoli, Cannavaro and Grava were exonerated on appeal this week and the club duly climbed to within three points of Juve, enjoying a share of second place with ambitious Lazio.
A vindicated De Laurentiis revealed he never applied the points penalty to his own version of the league table.
He told sscnapoli.it: "Without doubt I am very happy. This is not a victory for Napoli but for all of Italian football.
"I always believed and I still believe in justice. It was a correct and fair verdict.
"The league table was always the same for me, I just considered all the points we earned on the pitch. And so now it looks like I always thought it had.
"I'm happy for Grava and Cannavaro and for all the fans. No one deserved this infamy."
Arsenal manager Arsene Wenger confessed his admiration of free-scoring Uruguayan striker Edinson Cavani this week, but De Laurentiis is eager to retain his services.
"He's great, he's always given his all even when we were two points down in the league table," he added. "I hope he stays at Napoli for a long time, he could fly the flag for all Neapolitans."
Goran Pandev, Blerim Dzemaili, Valon Behrami and Morgan De Sanctis face late fitness tests ahead of the trip to Tuscany, while Fiorentina miss Michele Camporese, Mattia Cassani, Ahmed Hegazy and recent signing Giuseppe Rossi through injury.
La Viola were in the mix for a Champions League spot before two straight defeats kept the club treading water in fifth place.
A Coppa Italia quarter-final exit to Roma gave head coach Vincenzo Montella further food for thought, and he told La Repubblica: "This is a time when everything is going wrong.
"What is missing? I don't know, maybe we need strikers with different characteristics."
Fiorentina are keen to avenge September's 2-1 defeat at the San Paolo but the northern club are without a win over Sunday's opposition since a 3-1 victory back in March 2010.