Napoli would have won their first Serie A title since 1990 with a record six games to spare if they had beaten local rivals.
Napoli will have to wait at least a few more days to seal the Serie A title after drawing 1-1 with regional football rivals Salernitana, disappointing legions of fans of the southern club who had already started celebrating in anticipation of the championship.
The Partenopei could have clinched with a record six rounds to spare if they beat Salernitana on Sunday, but Boulaye Dia equalised for the visitors six minutes from time after Mathias Olivera had given Napoli the lead.
The result left runaway leaders Napoli 18 points ahead of second-place Lazio, who lost 3-1 at Inter Milan earlier.
Third-place Juventus could leapfrog Lazio and move into second if they win at Bologna later.
Napoli is attempting to win the Italian league for the first time since Diego Maradona led the club to its only two Serie A titles in 1987 and 1990.
Olivera scored just after the hour mark with a header, redirecting in a free kick inside the far post. Dia then dribbled by Napoli forward Victor Osimhen and unleashed an angled shot to equalise.
Napoli visits Udinese in its next match on Thursday, a day after Lazio hosts Sassuolo and Juventus hosts Lecce.
Napoli fans had been celebrating inside and outside the Stadio Diego Armando Maradona for hours before the match – raising their voices even louder after Lazio lost, which set up the chance for Napoli to clinch the title.
Bars and restaurants around the stadium heaved with people as cars, scooters and police vehicles tried to weave their way through a sea of fans and vendors who spilled out onto the road.
The city centre was closed to traffic shortly before kick-off, and more than 5,000 police officers had been deployed to maintain security, according to local newspaper Il Mattino.
The game had been moved back a day from Saturday on a request from local authorities to maintain public order. But Salernitana, which has not lost in more than two months, refused to let the celebration happen.
Urged on by a feverish crowd, decked out in blue and white, Napoli started on the front foot and almost went ahead seconds after kick-off when Osimhen headed Hirving Lozano’s cross just wide.
Osimhen, Serie A’s leading scorer, was the hosts’ only threat in what turned out to be a frustrating first half in which Salernitana defended deep and largely kept Napoli at bay.
The Nigerian striker had a couple of early chances for Napoli – one of them stopped by Salernitana’s standout goalkeeper Guillermo Ochoa, who recently went to his fifth World Cup with Mexico.
Ochoa also denied Napoli midfielder Andre-Frank Zambo’s chance in the first half.
There was also a long, curling effort from Napoli’s dribbling wizard Khvicha Kvaratskhelia that sailed high shortly after the break.
The match finally came to life with a dead ball opportunity, as Olivera beat several defenders to meet a corner from substitute Giacomo Raspadori and send it beyond Ochoa’s reach – causing an eruption of joy inside and outside the stadium.
Blue smoke engulfed the stands while fireworks audibly blasted outside the stadium, the acrid smell of spent firecrackers wafting through the ground.
Kvaratskhelia nearly doubled the advantage with a shot that missed just wide in the 80th minute. Minutes later, after Olivera was removed to make room for another defender, Dia equalised.
Still, Napoli fans applauded their team at the final whistle.
Inter’s victory moved them up to fourth, level on points with fifth-place AC Milan and sixth-place Roma.
Also on Sunday, Sassuolo beat Empoli 2-1 and Cremonese and Hellas Verona drew 1-1.