Frank Anguissa and Amir Rrahmani scored Napoli's goals in an eight-minute spell in the first half before Andrea Pinamonti cut the deficit early in the second period.
Fiorentina earlier remained on Napoli's heels after their 1-0 home win over Cagliari in their first league match since midfielder Edoardo Bove's sudden collapse last weekend.
Lazio will face either Inter Milan or Udinese in the quarter-finals.
Napoli coach Antonio Conte criticised the Video Assistant Referee (VAR) for not intervening to reverse a penalty that Inter Milan's Hakan Calhanoglu eventually missed in their 1-1 draw on Sunday.
Antonio Conte's resurgent side wrapped the match up inside the first half, courtesy of an early Romelu Lukaku goal and a sensational strike by Khvicha Kvaratskhelia.
Victor Osimhen has been sidelined by Napoli after the team he fired to Serie A glory just a over year ago left him both off their squad list for the 2024/25 campaign and potentially in season-long limbo.
Belgium striker Lukaku completed a permanent move to Napoli from Chelsea on Thursday, ending a long period of limbo with the Blues.
The futures of Napoli striker Victor Osimhen and England international Ivan Toney are set to dominate the final day of the European transfer window on Friday as Chelsea continue their frenzied pursuit of new signings.
Napoli manager Antonio Conte apologised to the club's fans after his side were humbled 3-0 at Hellas Verona in Serie A on Sunday and said he took responsibility for the loss.
A 2-0 win over relegated Sampdoria was little more than a hors-d'oeuvre before the real reason fans jammed into the Stadio Diego Armando Maradona -- to see their team lift the trophy for the first time in 33 long years
Spalletti has just led Napoli to the Serie A title for the first time since 1990 but there has been speculation about whether he would stay on.
The 24-year-old is now the highest scoring African player in the history of Serie A after overtaking George Weah and lapped up the applause of Napoli fans as the team did their post-match lap of honour
Napoli's champions returned home Friday after winning their first Serie A title in 33 years, greeted at their training camp by hundreds of jubilant fans following a raucous night of partying in Naples.
More than 200 people ended up in hospital overnight for injuries sustained during the celebrations, La Stampa said, from knife wounds to burns from firecrackers and asthma attacks caused by inhaling smoke from flares.
Retired midfielder Alemao, who won Serie A with Napoli in 1990 alongside late legend Diego Maradona, says he regrets his friend is not alive to celebrate the team's return to glory 33 years later.
Victor Osimhen said Thursday that he will never forget winning Napoli's first Serie A title in over three decades after his goal finally pushed southern Italy's biggest club over the line.
Napoli will have to wait at least one more day to be crowned Italian champions after Lazio beat Sassuolo 2-0 on Wednesday to reclaim second place in Serie A.
Leaders Napoli were held to a 1-1 home draw by Salernitana in Serie A on Sunday, extending the wait of Luciano Spalletti's side to seal their first title in 33 years.
Inter Milan came from a goal down to win 3-1 at home against Lazio in Serie A on Sunday, giving Napoli the opportunity to seal their first title since the Diego Maradona era this weekend.
