In the end, it was all just a little bit much. Manuel Locatelli could not hold back the tears, so he stood in the middle of the pitch at San Siro and blubbed. His chest was still shaking when the Mediaset TV crew arrived, the interviewer placing a gentle hand on his shoulder. “It’s all real, I want to tell you that,” said the kind man with the microphone. Locatelli forced half a smile, glanced at the ground and started to well up all over again.

This is what they mean on the peninsula when they tell you that “il calcio è emozione” (football is emotion). The Milan midfielder was not weeping out of sadness, not mourning some personal tragedy. He simply did not know what else to do after scoring his first goal for the club at 18 years of age, and doing so with an absolute screamer.

“It’s the moment that every kid hopes for in their life,” he said, voice wavering as he fought back the sobs. “When I realised where the ball was going, I couldn’t believe it. I started to run and then it was all real.”

What a way to get your first #SerieA goal! A fantastic strike from @acmilan's 18-year-old Manuel Locatelli. https://t.co/k5ePuVyNkl — BT Sport Football (@btsportfootball) October 2, 2016

He might not have been the only one who needed reassurance on that final point. An hour into Sunday’s game against Sassuolo, the Rossoneri had trailed 3-1 and appeared to be heading for yet another defeat to opponents who had beaten them four times in six Serie A meetings.

That was when Locatelli came on to replace Riccardo Montolivo. It would be a misrepresentation to suggest that his introduction turned this game around, but he did play a prominent role in what became a stunning reversal.

Milan got back into contention with a penalty that should never have been given. The referee Marco Guida was quick to point to the spot when M’Baye Niang went down while attempting to surge between two defenders, but replays made it clear that there had been no infringement. If anything, the Milan forward should have been penalised for pulling on the shirt of Sassuolo’s Pol Lirola.

Perhaps, in the not-too distant future, such mistakes can be avoided. Serie A was testing out a new video refereeing system at San Siro on Sunday, with two officials following the game on a monitor. But as this was only a trial – one of many to be conducted this season – they were not permitted to intervene in the match itself, instead only compiling notes to send to Fifa.

Sassuolo have every right to feel aggrieved. Compounding this error was the fact that they should have had a penalty of their own in the first half, when Matteo Politano dispossessed Gianluigi Donnarumma and was immediately brought down by the Milan goalkeeper.

Carlos Bacca made sure that no justice was served, converting Milan’s penalty with aplomb. Then came Locatelli’s moment. When a corner from the left was headed out only to the edge of the D, the teenager rushed forwards to meet it with a savage left-footed half-volley. You would never have guessed, as it flew into the top corner, that this kid prefers to hit them with his right.

Moments later, Niang looped a cross over from the left, and Gabriel Paletta rose magnificently to head Milan in front. The game was not over yet, and it took a strong hand from Donnarumma to keep out another late effort from Politano, but the Rossoneri clung on to secure a 4-3 win.

Milan defender Gabriel Paletta heads home the winner. Photograph: Matteo Bazzi/EPA

This was an important result for the standings. Despite a slow start, Milan are up to third, lending credence to Vincenzo Montella’s claims that they are ready to challenge for Europe. They are showing well against direct rivals, too. In the last three games, they have now beaten Sassuolo and Lazio, as well as drawing away to Fiorentina.

More than that, though, this was a win that might strengthen the club’s commitment to coherent team-building. Silvio Berlusconi, who celebrated his 80th birthday last week, has spoken often in the last few years of a desire to see Milan rebuilt around a core of young Italian players. Only now, as he sells the club, does the club seem to be actually moving in that direction.

It might be happy circumstance that got them to this point. Only the slow progress of Milan’s takeover prevented the club from investing more actively in the transfer market this summer. If Montella had been given free rein, then perhaps he would have demanded the signing of a more established name to compete with Montolivo for the creative role in central midfield.

As it is, that responsibility has fallen to Locatelli, a player who has been part of the Milan academy system from the age of 12. This was his fourth substitute appearance of the season, and it will be hard to deny him a first start for much longer.

Beyond the goal, he has demonstrated ample playmaking ability. It was Locatelli who released Luiz Adriano with a ball over the Fiorentina defence in the dying seconds of Milan’s draw at the Stadio Artemio Franchi – only for the Brazilian to be cynically brought down, without punishment, on the edge of the area.

He is not the only academy graduate getting a chance, either. Donnarumma has been a fixture of the Milan’s first-choice XI since last October, and 19-year-old Davide Calabria has started three games this season at right-back. Mattia De Sciglio has been around a little longer but at 23 is hardly a gnarled veteran, and he too was developed in-house.

Throw in the various fresh-faced talents that Milan have either signed or brought back to the club in the last 18 months – from Niang to Suso and Alessio Romagnoli – and it is easy to see why Montella might feel optimistic about the club’s long-term future. The teams he selects have been the youngest, on average, in Serie A so far this season.

If that means that one or two players struggle to keep a lid on their emotions then so be it. Where Locatelli got to fulfil his dream of scoring at San Siro on Sunday, Milan’s fans might be delighted simply to get the chance to watch a team that lives for these moments as keenly as they do.

Talking points

• What a game that was between Roma and Inter on Sunday night. How we got to half-time with only one goal being scored will forever be a mystery. Both teams were scintillating going forwards – Mohamed Salah’s sensational accelerations allowing him to get in behind the Inter defence time and again, while Éver Banega’s craft continuously unpicked the Roma back-line – right up until the final moment. The Nerazzurri are plainly improving under Frank De Boer, but it is troublesome that they have now conceded the first goal in eight games out of nine under his charge. As for Roma, they showed resilience in recovering after Inter equalised to get their noses back in front. But there’s still something troubling in their inability to protect a lead in the first place. But nine goals conceded in seven games are a concern, and with better Inter finishing that number would look a whole lot worse.

• There go Juventus, four points clear already after their 3-0 win at Empoli was followed by a surprising 1-0 defeat for Napoli away to Atalanta. The margin of victory flatters the Bianconeri, who made very hard work of things for more than an hour before rattling in all of their goals in a five-minute purple patch. But that’s the difference that having two players like Paulo Dybala and Gonzalo Higuaín up front can make. Empoli being dreadful helps, too, of course.

• No goal for Andrea Belotti this week, but no problem for Torino, who took their lead instead from Iago Falqué in a 2-1 win over Fiorentina. The Granata’s 13 goals, scored in seven games, represents their most prolific start to a season since 1976-77, when they finished a point behind Juventus in second place.

• A less encouraging historical note for Crotone – who suffered their sixth defeat of the season away at Cagliari and still have only one point to show for their first-ever season of top-flight football. That is the worst start any team has made in more than two decades.

• Don’t look now, but that’s two goals in as many starts for Diego Simeone’s son, Giovanni, at Genoa. His dad was full of praise for him during a conversation with reporters last week, noting that his progeny had “hunger, desire and is a lad who listens”. But he also insisted that they rarely talk about football together. “I’ve never liked to talk about aspects of his game,” said the Atlético Madrid manager. “We talk about life, which is much more important.”

Results: Atalanta 1-0 Napoli, Bologna 0-1 Genoa, Cagliari 2-1 Crotone, Empoli 0-3 Juventus, Milan 4-3 Sassuolo, Pescara 0-2 Chievo, Roma 2-1 Inter, Sampdoria 1-1 Palermo, Torino 2-1 Fiorentina, Udinese 0-3 Lazio