The Stadio Carlo Castellani held some unhappy recent memories for Napoli. It was here that their title challenge unravelled last April, as a 2-0 lead against Empoli in the 80th minute became a 3-2 defeat. They were authors of their own demise back then, the equaliser arriving when the goalkeeper Alex Meret dallied in possession and allowed Andrea Pinamonti to block an attempted clearance straight into his net.

Could they self-destruct a second time? They held an identical 2-0 advantage on Sunday when Mário Rui was given a pointless red card, kicking out at Francesco Caputo. Instead of wobbling, Napoli became even more dominant down a man, enjoying a solid five-minute stretch inside the final quarter-hour when they did not allow Empoli a touch outside of their own half.

Such is the dominance of Serie A’s champions-elect. Even in Italy’s most superstitious city, it no longer feels dangerous to define them as such. With Internazionale losing away at Bologna on Sunday, Napoli are now 18 points clear at the top.

They have lost once all season, against the Nerazzurri in their first game back from the World Cup break. Since then, they have piled up eight consecutive league wins – scoring 21 goals and conceding only two. There was one surprising slip-up in the Coppa Italia, Napoli exiting on penalties to Serie A’s last-placed team, Cremonese, but they had rotated all 10 outfield starters.

How did a club that have not won the league for 33 years reach a position where ending that drought feels like a formality by late February? Napoli were hardly pre-season favourites.

Luciano Spalletti reminded journalists at a press conference last week that many of them had tipped his side to finish outside the top four, but his team’s own fans had hardly felt confident. One interrupted his attempt to introduce the squad at an event in July, screaming at him to “wake up!”

The manager had been acknowledging the departures of the captain Lorenzo Insigne, the vice-captain Kalidou Koulibaly and the record goalscorer Dries Mertens in a single transfer window. Now Spalletti responded to his heckler, raising his voice as he insisted: “Others have arrived, bringing a fresh enthusiasm along with them. And more will arrive yet.”

New faces have indeed played their part. The signing of Khvicha Kvaratskhelia from Dinamo Batumi for a little more than €10m was possibly the best piece of business done by any club in Europe last year. His 10 league goals and nine assists tell only part of the story, missing out how he unbalances defences with two-footed passing and hip-swaying dribbles. Only Rafael Leão has beaten his man more often in Serie A this season.

Kim Min-Jae, too, has been colossal, signed for less than half of what Chelsea paid for Koulibaly and delivering even more consistency at centre-back. Other summer signings such as Giacomo Raspadori, Giovanni Simeone and Mathías Olivera have contributed regularly from the bench.

Yet nine of the players who started against Empoli were on the books already last year. This was pretty much Spalletti’s strongest team, the most common variations being to swap out Hirving Lozano for Matteo Politano (another returning player) on the right wing and Mário Rui for Olivera at left-back on European nights.

The real reasons for Napoli running away with the Scudetto are twofold. Most obvious to point out is the lack of competition. No other team are on course to finish with more than 74 points. Last season’s champions, Milan, endured a disastrous new-year wobble in which they dropped 13 in five games. Inter cannot seem to decide if they are the team who beat Napoli at the start of this year and Porto in midweek or the one that lost timidly to Bologna at the weekend. Juventus, even without their 15-point deduction, would not be any closer to first than those other two.

This lack of a domestic rival has led many to question how good Napoli truly are. Champions League nights continue to provide answers. After pummelling Liverpool, Ajax and Rangers in the group stage, Spalletti’s team made light work of Eintracht Frankfurt in the away leg of their last-16 tie. A 2-0 lead puts them on course to reach the quarter-finals for the first time in club history.

The biggest part of this puzzle is simply that the team have improved under Spalletti. There is a measure of good fortune. Victor Osimhen missed 39 games through illness and injury the past two seasons but only six so far in this campaign and none since early October. When fit, he can be one of the best centre-forwards on the planet. He has scored in eight consecutive league games and grabbed the opener at Frankfurt.

More than anything, though, Napoli’s players have bought into Spalletti’s coaching, adapting to a selfless and responsive style of play. On the surface, his team look quite predictable, lining up almost always in the same 4-3-3, but their approach to every game is shaped by the opponent, the emphasis shifting to exploit spaces as they appear.

Players are empowered to take risks and trust their judgment because they know they have teammates backing them up. The football analytics website Ultimo Uomo cited data from Statsbomb last week showing that only two players in all of Serie A have lost possession more often this season than Kvaratskhelia, but also that Napoli had won the ball back from opponents in the final third more than any other team.

Spalletti glowed on Sunday as he recalled a moment from his team’s previous win, away against Sassuolo. “We lost the ball at a corner,” he said. “What happened next, I’ve never seen anything like it in 25 years as a manager. Ten players in a frenzy, all running to make up the ground and get behind the line of the ball … that’s where you understand you have a team that is rock solid, who don’t want to give up one thing.”

The footage of that moment is quite something, Osimhen arriving in a makeshift left-back position as Napoli’s whole team sprint at full-pelt to plug the gaps. Sometimes, of course, they still need a bit of help from the sideline. Against Empoli, Spalletti stole the show when pitchside microphones picked him up yelling at Kvaratskhelia in broken English after the Georgian strayed offside.

By full-time, his only complaints were with Rui for that needless red card. Napoli had taken the lead on an own-goal, Ardian Ismajli deflecting Piotr Zielinski’s cross into his own net, and were 2-0 up by the 28th minute, when Osimhen pounced on the rebound after Guglielmo Vicario saved an initial shot from Kvaratskhelia outside the box. At no point did they really look like conceding. “The players know we have a really important opportunity,” Spalletti said of the Scudetto at full-time. “They need to do it for the fans. For their people.”

It is hard to imagine a scenario now where they wouldn’t manage it, the only real question being whether they will cross the line in April or May. If anything, the fear is that this monumental achievement, a third Serie A title for Napoli and a first since Diego Maradona left the club, could feel anticlimactic without a rival pushing them close.

From the lifesize cutouts of their starting XI that materialised in the Spanish Quarter this weekend to the street vendors already selling flags adorned with the number three and the pizza-makers trailing a special Scudetto recipe in national newspaper interviews, the people of Naples are already preparing to ensure a team and a city get the celebration they deserve.