Defeating Roma in the Derby del Sole took them 13 points clear of their closest rivals in the Serie A standings; their hosts, meanwhile, have lost back-to-back matches and sit just outside the drop zone.
Match preview
Napoli started the second half of their so-far spectacular season with another league win, as they dispatched southern rivals Roma at Stadio Maradona last Sunday.
After Victor Osimhen's outrageous opener set the tone for an absorbing affair, the Giallorossi equalised late in the second half to set up a grandstand finale; Giovanni Simeone then grabbed his fifth goal as a substitute this season to wrap up all three points for the Partenopei.
Simeone's 70th Serie A strike puts them out of sight at the summit, after reigning champions Milan also lost last weekend, and Inter are now their closest challengers.
Scoring so late so often is typical of champions, and Napoli have now netted 19 times in the final half-hour of games this term, with 12 goals arriving in the last 15 minutes. Meanwhile, at the other end, they have conceded only four times after the hour mark.
An average of 2.65 points per match is the best throughout Europe's top five leagues in 2022-23, and if the Campanian club were to maintain that rate they would post more than 100 points - only Antonio Conte's Juventus of 2013-14 have ever reached triple figures in the Italian top flight.
While they recently exited the Coppa Italia to a Cremonese side still to win in Serie A, such form makes Luciano Spalletti's men firm favourites to end a Scudetto drought stretching back 33 years, and they will also resume their Champions League campaign later this month.
Before now and then, though, a trio of apparently straightforward domestic fixtures await, the first of which sees Napoli visit a venue they have fared well at since Spezia's promotion in 2020.
Having been beaten by three goals in both previous Serie A meetings with Napoli at Stadio Picco, Spezia have also lost the teams' last two encounters without scoring following a 1-0 defeat in September's reverse fixture.
A solid if unspectacular start to the new year saw Luca Gotti's side visit the capital last month unbeaten in five league fixtures - having also kept successive clean sheets - but they then followed a 2-0 loss to Roma with the same scoreline in Bologna.
As a result, Spezia have now failed to find the net in three of their last four league games, and only Sampdoria have fired blanks in more Serie A matches overall.
After suffering their eighth away defeat from 10 attempts, the Ligurians can at least return to La Spezia this weekend, but they also face in-form Empoli as well as a wounded Juventus over the coming fortnight, so hosting free-scoring Napoli is far from ideal.
Any danger of dropping into the bottom three seemed distant before the winter break, but Spezia now sit just five points clear of 18th place with a resurgent Verona on their tails, and a relegation dogfight can no longer be ruled out.
Spezia Serie A form:
W
D
D
W
L
L
Spezia form (all competitions):
D
D
W
L
L
L
Napoli Serie A form:
W
L
W
W
W
W
Napoli form (all competitions):
L
W
W
D
W
W
Team News
In the fortunate position of having a fully fit and firing squad at his disposal, Luciano Spalletti is set to name a familiar lineup on Sunday, with Capocannoniere leader Victor Osimhen starting up front.
Following his exquisite strike last weekend, the Nigeria strike has netted 14 times in Serie A this season - already equalling his total haul of last term.
Giacomo Raspadori may therefore be consigned to the bench again, despite having scored three goals in three previous league meetings with Spezia, including his only top-flight goal this season. Meanwhile, Hirving Lozano and Matteo Politano once again scrap it out to start on Napoli's right flank.
By contrast with their visitors, Spezia face one of their toughest tests of the campaign with a lengthy absence list, featuring several important squad members.
Emmanuel Gyasi must serve a suspension, while fellow forward M'Bala Nzola joins Simone Bastoni on the sidelines due to injury. Even coach Luca Gotti has undergone a hip operation and may be unable to tread the touchline.
January signing Szymon Zurkowski is also ruled out, but more recent arrivals Eldor Shomurodov and Salvatore Esposito are likely to feature from the start.
Spezia possible starting lineup:
Dragowski; Amian, Caldara, Nikolaou; Holm, Esposito, Ampadu, Bourabia, Reca; Verde, Shomurodov
Napoli possible starting lineup:
Meret; Di Lorenzo, Kim, Rrahmani, Rui; Anguissa, Lobotka, Zielinski; Lozano, Osimhen, Kvaratskhelia