Did the title race turn on a clerical error? Matteo Politano looked set to join Napoli from Sassuolo this January, with terms reportedly agreed on a transfer worth €28m. The player was keen, yet, as the final seconds ticked away on deadline day, the paperwork never came through.

Two months later, Politano scored a goal that stopped Napoli from going back to the top of Serie A. The Partenopei travelled to Sassuolo on Saturday knowing a win would vault them into first – heaping pressure on to Juventus before their evening kick-off against a Milan who were yet to suffer domestic defeat in 2018.

A 46-point gulf separated Napoli from Sassuolo in the standings. Sure, the Neroverdi had beaten Udinese before the international pause – but that was their first win since Christmas. They had been thrashed 7-0 by Juventus as well as losing 3-0 to Atalanta and Lazio.

However, a 22nd-minute strike from Politano put Napoli on the back foot. The composure he showed to volley home the rebound from Federico Peluso’s header was conspicuously missing from the visitors’ attack. When Napoli did equalise, the last touch appeared to come off a Sassuolo defender, Rogério.

The game ended 1-1, leaving Napoli supporters to ponder how things might have gone differently if Politano were playing on their side. It is not only a question of his direct impact. If Napoli’s attack has lost sharpness at the tail end of this campaign, that might be because the front three of Dries Mertens, Lorenzo Insigne and José Callejón are spent.

This team has been unfortunate to lose Arkadiusz Milik to torn knee ligaments for large parts of the past two seasons. His impact off the bench on Saturday was notable. Having flashed a header just over at 1-0, he then struck the woodwork.

Yet even when Milik is available, there has always been a need for another option up front, a versatile all-rounder who could slot in on either flank. Politano was not Napoli’s first choice for that role but they turned to him after Bologna’s Simone Verdi rejected a move this January.

Perhaps Sassuolo were the wrong team to do business with. They have traded several players with Juventus in recent years, developing warm relations. Some have taken to describing the clubs as transfer market ‘allies’.

So when Beppe Marotta responded to the Politano speculation by saying the Sassuolo owner, Giorgio Squinzi, “has a solid club, he does not need to sell anyone”, there was a temptation to read between the lines. Was Juve’s CEO seeking to influence another club’s transfer policy?

The Sassuolo general manager, Giovanni Carnevali, has claimed his club never intended to sell Politano in January in any case. Yet Napoli’s owner, Aurelio De Laurentiis, tells things differently. By his account, a deal was reached on deadline day for a two-year loan – after which the move would become permanent. Napoli would send Adam Ounas in the opposite direction.

“At 10.48pm, or maybe 10.51, we sent a contract to Carnevali,” De Laurentiis said. “He told me that the lines were busy and nothing was coming through but then a contract arrived on my end for Ounas, missing the official stamp and signature. So I don’t understand: can we say this whole thing is a little mysterious?”

Not that De Laurentiis was too upset at the time. He argued Politano was neither as talented nor versatile as Verdi. “In my opinion,” he said, “I was throwing money out of the window.”

Those words have come back to haunt him. Instead of putting the pressure back on Juventus, Napoli could only sit and watch as the Bianconeri extended their lead atop Serie A.

They were not brilliant against Milan, although they did have the perfect start. Paulo Dybala opened the scoring after eight minutes with one of those nonchalantly superlative outside-the-box efforts that are becoming his trademark.

Juventus were closing in on a club record for their longest run without conceding in Serie A. Fittingly, it was a man who helped them to set the previous mark who stopped them 15 minutes short. Leonardo Bonucci, back on his old stomping ground, muscled in to head home a first-half equaliser.

He had been uncertain before the game about whether he would celebrate. Bonucci can hardly switch off the connection that he feels to the club with whom he won six consecutive league titles. It is only four Easters ago that he joined Juve fans on the Curva during a home game against Bologna.

Yet after hearing supporters sing abusive chants at him through the warm-ups and into the game, his mind was made up. He wheeled away performing his signature ‘wash your mouth out’ gesture.

For a long time, it appeared as though his would be the final word. Milan grew into the game and early in the second half looked most likely to win it. Hakan Calhanoglu hit the crossbar with a thunderous effort. Gigi Buffon had to react sharply to deny Suso.

Then Juventus found a way – as they usually do. Juan Cuadrado, making his first appearance in more than three months following hernia treatment, came on to head them in front in the 79th minute. Sami Khedira, a player many fans would happily have relegated to the bench after recent poor performances, provided the assist, before scoring himself to seal a flattering 3-1 score.

Three months on from transfer deadline day, Napoli’s title hopes hang by a thread. The reasons for their failure to sign Politano are murky. But the scale of the challenge they face in overhauling this relentless Juventus team remains as clear as day.

Talking points

• There was little solace to be found in an honourable defeat for Gennaro Gattuso. “It burns,” he said. “I can’t come down here smiling like a simpleton and say that I’m happy with the performance.” There is a recognition too that Milan’s Champions League hopes have been dealt a major blow. They are eight points behind fourth-placed Inter, so nothing less than a win will do in Wednesday’s rescheduled derby.

Milan’s head coach, Gennaro Gattuso, gestures during the defeat by Juventus. Photograph: Alessandro Di Marco/EPA

• Inter are looking sharp again, although they got some help in their 3-0 win over Verona. Ivan Perisic could have taken the credit for a quick throw-in that set up Mauro Icardi for a first-minute opener but he insisted it should go to the ballgirl whose rapid reactions put him in position to act.

• Roma’s draw with Bologna, coupled with Lazio’s 6-2 thrashing of Benevento, means the gap from third to fifth is back to three points. The Biancocelesti have scored 73 in 30 games.

• Raise a glass, or better yet a chair, to the memory of Emiliano Mondonico, who died last week aged 71. The former Torino coach is best remembered for lifting his seat above his head in protest at the referee during his team’s 1992 Uefa Cup final defeat by Ajax, but he was an irrepressible character at any time. Early in his playing career, he deliberately got sent off so he would be free for a Rolling Stones concert the following weekend. Buon viaggio, Mister.