Juventus’s first home game of the new season had already kicked off by the time Giorgio Chiellini arrived behind the dugouts at the Allianz Stadium. He raised an arm to acknowledge supporters singing his name, but needed both hands on his crutches as he lowered himself into his seat, trying not to place too much weight on a heavily strapped right knee.

Chiellini had ruptured his cruciate ligament in training one day before. A painful personal setback, and a potential catastrophe for his team. The Juventus captain is expected to be out of action for at least the next five months. For a 35-year-old footballer, such injuries can curtail a career.

His absence from the starting XI to face Napoli on Saturday was already a major setback. These were the champions’ closest rivals: the team that finished as runners-up in three of the past four seasons. Juventus were still adjusting to life under a new manager, Maurizio Sarri, who was unable to take up his own place on the touchline after contracting pneumonia in pre-season.

Antonio Conte calls for action after Cagliari fans racially abuse Lukaku Read more

It ought to have been a vulnerable moment for Italian football’s Old Lady. But sometimes La Vecchia Signora looks an awful lot like the Roman goddess Fortuna – the original Lady Luck.

Juventus opened the scoring in the 16th minute through summer recruit Danilo, who had only stepped on the pitch moments earlier as a replacement for the injured Mattia De Sciglio.

Of course, the goal was not all down to chance. Napoli were negligent, conceding from their own corner. Lorenzo Insigne’s shot was blocked by Leonardo Bonucci, and his teammates were too slow to react as Danilo released Douglas Costa on the counter before arriving in the penalty box to convert the return pass. He had been on the pitch for 29 seconds in this, his Juventus debut.

Defence was supposed to be a strength for Napoli this season, after they signed Kostas Manolas to play alongside Kalidou Koulibaly at centre-back. Yet the latter player was left flat-footed as Gonzalo Higuaín made it 2-0 with a sharp turn and finish moments later. The game looked to be up when Cristiano Ronaldo added a third shortly after the hour mark.

Instead, Napoli would drag themselves back level during a remarkable 15-minute burst, then throw all their hard work away in injury time. Manolas headed in from a free-kick, before Hirving Lozano – making his own debut as a second-half substitute – slotted home from a José Callejón cross. Carlo Ancelotti raised both eyebrows as Giovanni Di Lorenzo arrived at the back post on another set-piece. Suddenly, the score was 3-3.

Facebook Twitter Pinterest Giorgio Chiellini watches from the sidelines in Turin. Photograph: Isabella Bonotto/AFP/Getty Images

The comeback narrative was laced with juicy subplots. Chiellini’s replacement, the €75m summer signing Matthijs De Ligt, had endured a calamitous debut: losing his man on all three of Napoli’s goals. We can be lenient in our judgements of a 20-year-old defender playing in a new team and an unfamiliar league, while still acknowledging that the captain is going to be missed.

Juve’s best player was Higuaín, a defining figure in the recent rivalry between these two clubs. Sarri’s first title challenge with Napoli was built on the striker’s record-breaking 2015-16 campaign, before the Argentinian joined the Bianconeri. The goals he scored over the next two seasons were crucial to keeping the Scudetto out of his former manager’s hands.

Now their fates are once again intertwined. Few people expected Higuaín to have a role at Juventus following disappointing loan spells at Milan and Chelsea, yet he started at centre-forward on Saturday just as he had on the opening weekend. Even before scoring, he had created problems for Koulibaly with intelligent movement outside the penalty box. He teed up Sami Khedira for a golden chance that went begging at 2-0, as well.

Sign up to The Recap, our weekly email of editors’ picks.

At one point, Higuaín was applauded even for a missed pass, because fans recognised his intent. A louder ovation was offered when he came off in the 76th minute.

Di Lorenzo’s equaliser arrived soon after, but there was a further twist yet to come. In injury time, Juventus won a free-kick 40 yards from goal. Their own players barely reacted as Miralem Pjanic heaved a last hopeful ball into the Napoli box. Koulibaly, however, attacked it decisively at the near post. The ball caught his shin and flew into the top corner of the net.

Premier Sports 📺 (@PremierSportsTV) Kalidou Koulibaly with an own goal in stoppage time! 🤯



You couldn't make it up 😳



UNBELIEVABLE!!#SerieA pic.twitter.com/2OH13SUrlU

It was a freakish mistake that capped a night to forget for a player who has known the very different emotion of scoring a 90th-minute winner for his own team at the Allianz Stadium. Koulibaly was Serie A’s best centre-back last season, but this was an occasion when – with Chiellini watching from the stands – both teams forgot how to defend.

Premier League, La Liga, Bundesliga, Serie A and Ligue 1 top scorers 2019-20 Read more

The Juventus captain came down on his crutches to console his opponent after the final whistle: a show of empathy from one great player to another. “I used to hate him,” confessed Sarri’s No 2, Giovanni Martusciello. “Because playing against us he was a real ball-buster. But I have got to know an extraordinary lad … after the injury, he was the one who gave us courage.”

Juventus will need more than just that to win a ninth consecutive Scudetto. They can draw plenty of encouragement from an early win over a direct rival, but for a team that only conceded 13 goals at home last season to ship three in their first game without Chiellini ought to set alarm bells ringing as well. There is little that feels settled about a team whose new manager has thus far been forced to work at arm’s length. With Antonio Contes Inter sitting alongside them at the top and Napoli boasting plenty of room for growth, there is much that feels unfamiliar yet.

Talking points

• A new campaign, but the same grim story at Cagliari, where Romelu Lukaku was targeted with racist abuse – just as Moise Kean was last season and Blaise Matuidi the year before. At least this time we did not hear any Inter players seek to apportion blame to their teammate. But what should we expect, given that no punishment was handed down to Cagliari for the previous incident – after which the club’s president, Tommaso Giulini, rejected all accusations of racism and accused the media of false moralising?

• Two goals in two games for Lukaku. His was not an especially well-rounded performance, but he did help win the penalty, which he converted, with his through-ball for Stefano Sensi.

Facebook Twitter Pinterest Romelu Lukaku scores from the penalty spot. Photograph: Fabio Murru/EPA

• A surreal Rome derby on Sunday, with the two teams combining to hit the woodwork six times – and five in the first 25 minutes alone. Lazio were better and look more ready to challenge for the top four. Joaquín Correa and Ciro Immobile are ever more comfortable, and dangerous, as a front two. But Roma are great fun to watch under Paulo Fonseca.

• Level with Juventus and Inter are Torino. Walter Mazzarri’s team bounced back impressively from their Europa League exit by recovering from 2-1 down to win at Atalanta.

• An eye-catching win for Sassuolo, too, who thrashed Sampdoria 4-1. Samp, of course, managed by their former manager Eusebio Di Francesco …