Ruben Amorim had waited a lifetime for his first Milan derby. As a kid growing up in Lisbon, he supported two football teams. There was the local one, Benfica, whose games he attended so early in life that his father has recalled changing nappies in the stands of the old Estádio da Luz. And the other one that captivated him from overseas.

“I remember watching tapes of that Milan team with [Paolo] Maldini, [Franco] Baresi, [Ruud] Gullit, [Frank] Rijkaard, [Dejan] Savicevic,” Amorim told Portuguese newspaper Expresso back in 2017. “My childhood dreams were to play for Benfica and Milan. I’ve fulfilled one. Now I suppose I’ll have to become a coach for the other!”

It took him another nine years to achieve that ambition. The Milan side he inherited this June did not look like the continental conquerors he used to admire on VHS. This version had just missed out on the Champions League for a second season running. Its hoped-for star of this decade, Rafael Leão, was ready to move on amid laments of unfulfilled potential.

Still, from day one, Amorim has given off the air of a cat who got the cream. It was tempting to infer some relief at moving on from an unhappy chapter at Manchester United. Certainly it can’t have hurt that Milan’s owners backed their new manager to a tune of more than €160m on transfer fees in the summer window.

But there was something in there too, of a person fulfilling a promise they made to their younger self. “Everybody knows Milan is one of my clubs since I was a boy,” said Amorim. “In my time as a young boy, Milan was the strongest team in Italy. And calcio was the best league in the world.”

Serie A lost that title some time ago. No Italian team has won the Champions League since 2010, and no player representing one has been awarded the Ballon d’Or since 2007. The Premier League long ago surpassed all rival competitions for TV revenues and spending power. Only a handful of super clubs elsewhere have kept up.

And yet, Serie A is having some kind of moment. Its reputation as the home of dour catenaccio is as outdated as Amorim’s old VCR, but things have spun especially far in the opposite direction this season, with an average of 3.18 goals per game. Italy’s top division has become home to some of the giddiest attacking football on the continent. Through almost 10 completed rounds there have been two 0-0 draws.

Amorim’s Milan have played their part. On Wednesday night they suffered their first league defeat, a barmy 4-2 loss at home to Bologna in which they fell behind early, came back to lead before half-time then collapsed after the interval. Their manager cited exhaustion. An ominous thought, leading into Saturday’s derby. Inter had dropped just two points all season. Even their one draw felt more like a win, coming from two goals down to get a result away to Roma. Reigning champions, who reinforced the deepest squad in Serie A with the English trio of Curtis Jones, John Stones and Djed Spence in the summer, the Nerazzurri have been strong favourites to retain their title.

But after waiting a lifetime for a part in this fixture, Amorim was never going to arrive unprepared. If anything, the loss to Bologna might have been influenced by his keeping one eye on the derby. Luka Modric and Christian Pulisic were both left out of the starting XI in midweek, coming on only as second-half substitutes. Both lined up at kick-off against Inter. So did several other starters who had been deemed unfit even for a place on the bench against Bologna – Mario Gila, Adrien Rabiot and Diego Moreira. Amorim sprung a surprise on top of that by naming the 20-year-old Sankhoun Diawara, whose only previous Milan start had been at centre-back, as his left wing-back in a 3-4-2-1.

The manager has shown more tactical flexibility at Milan than he did in Manchester, alternating his back three with a four. In the biggest game of his Milan tenure to date, however, Amorim returned to what he knows best. And Cristian Chivu copied him.

Inter’s manager was grappling with an availability crisis up front. Lautaro Martínez has been out for weeks with a hamstring strain, while Francesco Pio Esposito and Ange-Yoan Bonny were unfit to start due to a virus. Chivu adapted by pushing Andy Diouf, a former midfielder who has been thriving at wing-back, forward to play on the right shoulder of Marcus Thuram, with Petar Sucic on the left.

But where the Nerazzurri looked unsure of themselves in a new system, Milan were straight into their stride. Pulisic put them in front in the fourth minute, his thumping header from Moreira’s cross the culmination of 80 seconds of unbroken possession. Rabiot then made it 2-0 in the 10th minute with a magnificent first-time flick across his body at a corner.

Inter’s defending, on both occasions, was horrendous, but that can be acknowledged without diminishing Milan’s design. The Rabiot goal was a rehearsed training ground routine, Diawara crossing paths with the Frenchman and blocking Hakan Calhanoglu’s attempts to track. Moreira was also flawless in his deliveries. The derby became his breakout moment, showing why Milan spent more than €50m to sign him from Strasbourg this summer.

Inter have recovered from losing positions five times already in this Serie A season, and three times from 2-0 down. They were threatening to repeat the trick after Alessandro Bastoni pulled a goal back from a corner. Spence forced a sensational save from Mike Maignan. But Milan won a free-kick, 20 yards out on the right. Moreira asked Modric to let him take it, then whipped a left-footed shot over the wall into the near side of the net.

The game finished 3-1 to Milan, Inter’s first league defeat and a huge lift for Amorim. Despite being unbeaten themselves before the midweek loss to Bologna, the Rossoneri have not always convinced. Even when controlling the tempo of games, they seem to lack clarity in the final third. Gonçalo Ramos, the club’s record signing, has not looked a natural fit as a lone striker, dropping deep too often when his team needs a presence inside the box. He has scored just twice in 10 starts since his €73m from Paris Saint-Germain.

Even this win raised questions. Can it really be the long-term vision for Moreira, the right wing-back, to frequently hold a position on the pitch higher than the centre-forward?

Amorim was quick to insist that nobody should get carried away on Saturday. He expressed delight for supporters and described the experience of his first Milan derby as unlike any other game he had ever been a part of. But he also said Milan had only been good, not great, and noted that the three points here were only the same number they would have got by beating Bologna.

A sensible line to take. Milan have dominated this fixture lately – winning the last four derbies across all competitions and staying unbeaten in the last eight. Yet they have not finished above their neighbours since 2021-22, their last Scudetto-winning campaign.

Still, beating your greatest rival is always better than the alternative. The club’s owner, Gerry Cardinale, has been vocal in backing the new manager, telling La Gazzetta dello Sport last week that he was all in on “Amorim ball”. But in the week that Milan and Inter jointly presented plans for the new stadium that will replace San Siro in 2031, this result added weight to his assertion that the Rossoneri can contend for a Scudetto too.