If Napoli win the Scudetto in May, we will perhaps look back on last weekend's win in Bergamo as a significant moment. When you lose three of your last four games to Atalanta and have to go and play at the Atleti Azzurri d'Italia just 19 days after they knocked you out of the cup in your own backyard, it counts as a serious examination of your title credentials. And Napoli did not give Juventus the satisfaction of slipping up. Dries Mertens performed an exorcism. His goal chasing away the evil spirits that so often frighten Napoli when confronted with teams coached by Gian Piero Gasperini.

You have to salute their character. The atmosphere was once again pretty hostile in this part of Lombardy. There were chants discriminating against people from the south of Italy. Defender Kalidou Koulibaly was once again subjected to racist abuse and a bottle, believed to contain urine, was also thrown in his direction. Referee Daniele Orsato neglected to include it in his report despite Allan's repeated efforts to bring it to his attention.

It could all have left a bitter taste in the mouth were it not for the sweetness of the win. Napoli lost here last season. You may recall Atalanta did the double over them in the league and when the fixtures came out this year you can bet Maurizio Sarri and his players looked upon these two league games against the Bergamaschi as a couple of stress tests. To obtain six points out of six then, particularly when Atalanta's other wins against Roma and Milan are still fresh in the mind, definitely does a great deal not only for Napoli's self-esteem but general confidence in them as bona fide pretenders to Juventus' crown.

The wobble they had at the start of December, when people seriously started to question them, looks to be over. The problems that provoked it haven't gone away. But just as Sarri improvised last year, reinventing Dries Mertens as a centre-forward after Arkadiusz Milik's knee injury, he has found a way to keep this team racking up points at an unprecedented rate. Napoli are still without star left-back Faouzi Ghoulam and if his absence has been less conspicuous in recent weeks that's entirely down to Sarri.

Napoli's win at Atalanta was just the latest indication they might just have what it takes to be champions. MARCO BERTORELLO/AFP/Getty Images

It's no small feat. Such a big part of their attacking play, Lorenzo Insigne can't come inside as much without Ghoulam, which in turn affects Mertens who no longer has someone nearby to play those lightning fast combinations with. Mertens' goal on Sunday was his first since late October, bringing a 910-minute drought to a welcome end.

A lean spell as long as that from your top scorer would usually compromise a title challenge. But not Napoli's. More attention has been placed on set pieces and Sarri has turned centre-back Koulibaly into a centre-forward. The Senegal international has scored four goals this season and gives Napoli a presence they otherwise lack in the box with the little guys up front.

It was also great that Marek Hamsik broke Diego Maradona's club all-time goalscoring record when he did. The weight seems to have been lifted off the Napoli captain's shoulders, which were leapt on repeatedly as 2017 drew to a close. The Slovak finished the year on the scoresheet three games in a row. The aforementioned Allan has also been magnificent.

Still, Sarri would be the first to admit goals are not coming as easily to Napoli as they were in the first three months of the campaign. Top scorers last season, unusually for them their attack ranks only third at the moment behind those of Lazio and Juventus. Ghoulam's imminent return should help in that regard as will Milik's but the principal reason Napoli still have people convinced is the defence, which is currently Italy's best. Six clean sheets in 10 and three on the bounce, Napoli was able to maintain their momentum despite struggling to score. Koulibaly has been imperious and the offers Napoli expect to field for him in the summer will make Virgil van Dijk look cheap.

The resilience of this team continues to go overlooked. Napoli won only one game 1-0 all last season. This year it's already happened four times. They have come back from behind on five occasions too, including twice in the same game against Sampdoria. That takes mental toughness as does going all of 2017 undefeated on the road. What Napoli are doing is extraordinary. Look at it this way, last year they set a new club record points total and yet today they have 10 more points than they did at this stage last year. They are still in front of Juve even though the Old Lady is also doing better than she did at this stage of last season.

Napoli were able to remain top despite a recent 910-minute goal drought from top scorer Dries Mertens. Robbie Jay Barratt - AMA/Getty Images

For all the strides Napoli have made, though, particularly when it comes to holding their nerve, stopping Juventus from getting under their skin is paramount. Sarri complained at the weekend about having to play after the Bianconeri in each of the next eight matchdays. It sent the wrong message. Does he not think his players can handle that sort of pressure? It seems odd considering the examples of mental fortitude Napoli have displayed thus far. It's also their own fault for dropping into the Europa League, which won't be a priority with Napoli going full tilt on ending a 28-year wait for the title. And as the league outlined in a statement this week, Napoli have played before Juventus in 14 of the last 19 matchweeks.

Sarri's mind games did not stop there either, though. When asked about Napoli's chances of signing Sassuolo winger Matteo Politano this month, he downplayed the idea, joking that "Marotta says he is 'unsellable'." Beppe Marotta, the Juventus general manager. Sarri's insinuation was clear. Juventus and Sassuolo have done a lot of business over the years and enjoy a close relationship. But could Marotta really exert enough pressure on Sassuolo to stop them from letting Politano join a title rival? "It's absurd," Sassuolo's sporting director Giovanni Carnevali said.

In the meantime, Napoli have turned their attention to Ajax's Amin Younes who was due to join in the summer for free but will now arrive this week for €5 million. Reflecting on their recruitment strategy, if Politano was never on the market in the first place, Younes ranks as Napoli's second choice after Simone Verdi who turned them down and will stay loyal to Bologna at least until the end of the season. Bologna handed him the captain's armband as a token of their gratitude last weekend, which clearly inspired Verdi. He set up all three of the Rossoblu's goals in a thumping 3-0 win against Benevento.

As fate would have it, Napoli meet Bologna at the San Paolo this weekend, the first of three games at home from their next four. It's up to them to show Verdi what he's missing out on, which, if everything goes to plan, could include a Serie A winners' medal...