Those who have worked under Antonio Conte talk of a moment, discernible in the hours of physical drills or monotonous tactical planning back on the training ground, when the penny drops. It is as if they have all experienced that same flash of realisation, the point when any resentment that has built up at the feverish workload or incessant reminders of on-field duties gives way to acceptance of the Italian’s genius.

His players have all felt it, whether they were turning out at Arezzo at the foot of Serie B or Juventus at the pinnacle, for Bari and Atalanta in Italy’s second tier or, since last summer, with Chelsea in the Premier League. “It’s as if it suddenly dawns on you that, by following him, you can go places,” said Luca Marrone, an Italy Under-21 midfielder who played under Conte at Juve. “He’s the toughest coach you could imagine, someone who demands everything of his players, his staff, the doctors, the physios … everyone at the club has to give 100%.

“It takes time to accept the sheer amount of work he is asking of you. Everything he does, in preparation or tactical organisation, is done with maniacal precision and attention to detail. It can be overwhelming at first. But, when you realise by buying into it you can win things, you follow. He is a perfectionist. The best there is. The No1.”

Chelsea travel to Manchester United, and their latest reunion with José Mourinho, the most successful manager in their history, on Sunday with Conte tantalisingly close to achieving what most in this country thought improbable upon his appointment last summer. Recognition of this team’s progress requires the context of the mess the Italian inherited.

Last season was the worst of Roman Abramovich’s ownership, a tale of the unravelling of Mourinho’s second spell in charge, dissent in the stands and crass underachievement on the pitch. Guus Hiddink, back as interim, had instigated a lengthy unbeaten run crammed with draws but the 10th-place finish, 31 points behind Leicester City, was the worst title defence since that of Leeds United in the Premier League’s first season. Players were unrecognisable and faith in their quality had eroded. Conte often reminds the world that no one expected this club to challenge this year. Even the hierarchy have been pleasantly surprised at the pace of progress.

Back in Italy few have batted an eyelid. They were intrigued as to how their compatriot would fare in a new environment and with his grasp of the English language still in its infancy. But, deep down, they always knew the man who had restored the scudetto to Juve, and had overseen the Azzurri’s development from group-stage failures at the 2014 World Cup to one of the most impressive teams at Euro 2016, would triumph. Quality will out. Once the players recognised the value of his instruction, they would prevail.

The intensity and tenacity of the man had already been shown in pre-season, whether in Austria or Cobham via the United States, to fuel suspicions he would succeed eventually. He had arrived a week after Italy’s exit from the European Championship, a man eager to fling himself into a new role. “His secret has always been his enthusiasm,” says Massimo Carrera, Conte’s assistant at Juve from 2011 to 2014 and now coach of Spartak Moscow.

“He has this infectious energy which helps bring out the best in any player. Some might be a little unhappy to start with because they have to work so hard – his training methods are so demanding, so intense – but, when they understand all this effort brings rewards, those are the same players who ask if they can train even harder. This is Conte’s greatest triumph, and I’m convinced it’s what happened at Chelsea.

“Antonio is the best in the world because, when his players take to the pitch, they know everything about their opponents. Absolutely everything. Every little weakness or strength down to the tiniest detail. This obsessive attention to detail is his great weapon. I remember we’d spend weeks on end preparing for games. With him, a player has absolute certainty. He knows his opponents, their weak points, where to attack them, what to look out for. On the pitch they only have to play. They will never, ever, be taken by surprise.”

Reaching that point, where the playing staff accept the constant demands for “work, work, work” (a word the Chelsea manager used 32 times in a little under an hour at his first press conference), can be painful at times. Many, from Eden Hazard to Diego Costa to Cesc Fàbregas, took time to be convinced. The stop-start nature of training games, as the manager interrupts play to bark instructions or remind personnel they have wandered slightly out of position, grated with some. The same has happened at all his clubs. Marrone described his approach “come un martello” – “like a hammer”. “Until you get something right, he keeps you out on the training pitch to try and try again,” says the midfielder, who is on loan at Zulte Waregem in Belgium.

“Conte’s training sessions are incredible,” Carrera says. “He spends hours and hours talking to his players, wanting to prepare them for everything. And he does exactly the same with his technical staff. When he comes up against the smaller teams, the weaker sides, he demands maximum concentration. If his team loses, he gets so angry.

“He’s only able to accept defeat if his players gave absolutely everything on the pitch. But he’s an incredible motivator, a really passionate guy. He builds a great relationship with every single player, spending hour after hour talking with them, transmitting his ideas. Players follow him.”

The Italian undoubtedly taps into his own experiences as a player in building up that relationship with his squad. He has always had a presence. Giorgio Perinetti, sporting director at Venezia but on Juve’s technical staff during Conte’s playing days in Turin, recalls the midfielder imposing himself as the strongest voice in a dressing room that included Zinedine Zidane, Didier Deschamps and Edgar Davids. “Carlo Ancelotti and Marcello Lippi would ask him to transmit their ideas to team-mates on the field because they trusted him,” he says. “He is so single-minded. And his work ethic is so strong. Leonardo Bonucci [the Juve and Italy defender] says that when match day comes for a team coached by Antonio you already feel as if you’ve played the game. In Italy, he brought a new intensity and energy to the game in a country where the rhythm has been so slow.”

He has also brought an emphasis on tactical cuteness that stood him apart even at a club previously coached by Mourinho. If the first few weeks of the season had seen Conte gauging his squad’s capabilities – and adjusting to a frustrating summer in the transfer market – then those defeats to Liverpool and Arsenal in the autumn convinced him something more radical was required.

Antonio Conte with Arezzo in 2007. Photograph: Massimo Pinca/AP

So much has been made of the switch to 3-4-3 as innovative when it was only startling because Chelsea were previously so set in their ways. Just as significant was Conte’s willingness to adopt a system that senior players, from John Terry to Branislav Ivanovic, or even Pedro to Willian, might not be naturally suited or not even feature.

Yet the Italian felt sufficiently empowered by the encouragement he received from Abramovich, the director Marina Granovskaia and the technical director, Michael Emenalo, to instigate the changes and the instant results – Chelsea have won 25 of their 30 games playing three at the back – tell their own story.

“Impressing his vision on big-name players in the Premier League was a challenge, and he struggled at first,” says the former Chelsea striker Hernán Crespo, a veteran of spells at six Italian clubs. “But he eventually found a middle-ground. Conte made the defensive group more solid, then organised his midfield. The platform allowed his offensive players, Hazard and Pedro, more freedom to express their talent.

“He is replicating what he did at Siena and Bari, ensuring his players know exactly where to be on the pitch at any one time, and proving yet again that managers schooled at Coverciano [the Italian FA’s headquarters in Florence] are the best, tactically, in the world.”

A lack of European football has granted him empty weeks to transmit his instruction, with the club’s video analysis department – where his younger brother, Gianluca, plays a significant role – permanently rushed off their feet. Training sessions have been recorded and studied meticulously by the manager, who refers back to footage from drills and matches in his team meetings back at Cobham’s media suite.

“My players were not used to the videos at first,” Conte has said. “It was very difficult and after five or 10 minutes they would drift off. But then we started to see it in the right way. We watch games not to find out who was at fault, but because we can improve.”

Marrone remembers a 2-0 defeat the manager “took really badly” while at Juve to the extent that, half an hour after the final whistle, he “took us all off and made us watch the match again to point out everything that had happened”. There is no escaping in this regime.

Yet players quickly recognise one of their own. This is a manager who acknowledges some of their more selfless work out on the pitch. Costa, with whom Conte has had his differences, is regularly taken aside and praised for the aggressive runs, plenty of them fruitless, which set the tone for the whole team’s approach. The manager goes out of his way to know how every player is feeling, whether he is fatigued or distracted, at ease or on edge and can empathise with them given his own 19-year professional career.

The regular team meals – there was another in a London restaurant before the trip to Old Trafford – have helped bond the group. Back in the summer it had been his idea to hold a barbecue for the first-team squad, staff and their families, with the groundsman at Cobham marking out a five-a-side pitch by the main building for the players’ children, overseen by Chelsea Foundation coaches, to stage their own game while training concluded. Costa, even exhausted after a 90-minute session, ended up joining in with the kids while Conte looked on approvingly.

He has given all a platform upon which to thrive and helped to rejuvenate a club in the process. The little touches behind the scenes have made as much of an impact. The Italian’s late decision to attend the staff Christmas party, despite already having recorded a video message to be played in absentia, said a lot for the sense of responsibility he has embraced. Just as revealing were the bottles of wine and prosecco he sent to all members of staff, together with a signed note thanking them for their hard work and carrying the quote, attributed to Hannibal when his generals told him it would be impossible to cross the Alps by elephant: “We shall either find a way or make one.”

That sums up Conte’s attitude and, until now, he has been true to the Carthaginian’s word. That dogged pursuit of the title will resume at Old Trafford but the destiny of the trophy has long since felt like a foregone conclusion. Those who knew him saw this coming. Last summer, Conte had spoken to Álvaro Morata and his entourage about the possibility of swapping Real Madrid for Chelsea. The Spanish club eventually opted against a €60m sale but Morata, who had also spoken directly to Mauricio Pochettino at Tottenham, and his family had still been left with one certainty. “I remember talking to my dad and him saying: ‘This guy’s going to win the league there,’” the forward recalls. Morata Sr is about to be proved right.

Additional reporting by Simon Burnton and Fabrizio Romano