"My wife [Karina] said, 'You have to go'. I looked at Jesus and he said, 'I agree, we have to go'," Pochettino later recalled.

The Argentine had been offered the Southampton job but, not speaking a word of English, he worried it was too soon. Karina and Jesus Perez, his assistant, knew otherwise.

On Sunday, Pochettino will return to St Mary's as Tottenham manager.

Of all the tiny chances that led him to England, meeting Perez in July 2010 is perhaps the most significant. The Spurs manager bonded with Miguel D'Agostino and Toni Jimenez, his other coaches, in his playing days but was thrust together with Perez at Espanyol.

Initially hired as an analyst by sporting director Ramon Planes, Perez immediately earned the manager's trust. He was soon Pochettino's right-hand man, becoming the final member of the backing trio that has accompanied the headline act to the top of English football.

"As a unit, the four of them are very tight. They've all got the same beliefs on football but also on how to go about your life," former Spurs midfielder Ryan Mason told ESPN FC. "They're all on the same page. They do everything together. I think the four of them are best mates."

Professionally, and perhaps personally, Perez is the closest to Pochettino, who describes the Spaniard as "an extension of myself". Their family homes are a stone's throw apart and they often share lifts to and from Spurs' Enfield training base, where they can spend a 15-hour day in tandem.

Pre-Pochettino, Perez was a journeyman fitness coach, working at a number of Spanish clubs and in Saudi Arabia. His meticulousness and professionalism earned him admirers, including two-time Real Madrid head coach John Toshack, who spent four months with Perez at Real Murcia in 2004.

An old-school manager who played under Bill Shankly and Bob Paisley at Liverpool, Toshack traditionally mistrusted preparadores fisicos, particularly those, like Perez, who had never been players.

"Jesus did impress me in a way that I hadn't been impressed by those kind of people previously," Toshack said. "Whereas I normally would have taken control of all the physical work myself, I was quite happy to let Jesus get on with it. He was very thorough, very professional in everything he did and a learned type. I remember his attention to detail. I'm not surprised he's pushed on and done as well as he has with Pochettino."

By the time he had persuaded Pochettino to move to England, Perez was the manager's most trusted confidant, responsible for so many aspects of his philosophy. His qualities were immediately obvious to the players at Southampton and Spurs, as Pochettino and his staff took no time in winning disciples.

"I still hear Jesus' voice now," Mason, who spent two years playing under Pochettino and Perez, said. "When I'm training or playing and my body is telling me, 'You're knackered', I still hear his voice saying, 'You're a strong boy, Mase!' That stuck. It's always there. He's amazing at his job, he really is.

"They made you believe in your body and trust your body, and push it to a level which you may not have reached [otherwise]," added Mason, now at Hull City. "It's easy to think you're tired and that you don't have anything else in you. But they train your brain to tell your body you're not tired.

"Everything was positive. There was never anything negative. Your brain gets used to hearing this positivity all the time."

Perez, a meticulous organiser, distributes monthly training schedules to the squad weeks in advance. He is Pochettino's link between almost every department at the club, condensing information for the manager. His responsibilities include pre-match tactical presentations and morning one-on-ones with every player.

Pochettino has described him as "my eyes and ears" and Perez has an air of omnipotence that has occasionally left senior players amazed. If someone arrives in a flashier car or even wearing an expensive new watch, Perez will notice. Victor Wanyama, the Spurs midfielder, has described him as "mad".

"He knew everything! I'm not a clubber, I don't go out drinking, so I felt pretty safe," Mason said. "But I'm sure if a couple of the lads fancied a night out and the odd drink, Jesus would know about it. He always knows. Sometimes he probably chooses not to bring it up. He covers everything. You wouldn't cross him but, at the same time, he's a great human being.

"They understand the other side of the game, they understand the mental side, the stress you go through away from the pitch. Everything is geared towards the mental. It's not just solely physical or tactical -- it's your life as well and how you go about it daily. They cover every angle."

Perez notes every meal, every drink and every disturbed sleep, and each training session is filmed. Pochettino's three coaches have thousands of videos on their MacBooks, dating to Espanyol, when D'Agostino had to climb a scaffold pole to set up the camera. While team talks are led by Pochettino, Perez is never far away and he is always present when the manager speaks to a member of club staff or the media, translating when necessary.

Unlike his idol, Sir Alex Ferguson, Pochettino never wants to change his staff and he is the only manager in the Premier League who uses "We" rather than "I" and negotiates the contracts of his coaches, as well as his own.

"I'm surrounded by three guys who are hungry to improve and learn, so I don't need to make changes," he has said. "It's not the 'Mauricio Pochettino method': It's a group effort."

Larger-than-life Jimenez, an Olympic Gold medalist, and D'Agostino -- who Pochettino bonded with as a teenager during Marcelo Bielsa's "interminable" training sessions at Newell's Old Boys -- are well-liked and influential figures, but Perez is Pochettino's rock.

The manager has said that while Karina provides order in his home life, Perez does the same at work. As he returns to Southampton after half a decade in England, he can reflect, in more ways than one, that he would not be here without them.