The meeting went long into the night, according to legend.
It was October 2006 and a 35-year-old Pep Guardiola, still playing for Mexican outfit Dorados de Sinaloa at the time, had travelled over 5,000 miles to pick the brains of a manager whose work he had long admired from afar. He wanted advice, to find out whether a move into management was right for him.
Marcelo Bielsa was in the middle of a lengthy period of self-reflection having left his role as coach of Argentina's national team two years earlier. But he was happy to welcome Guardiola and his friend, the writer and film director David Trueba, to his home outside Buenos Aires to answer questions.
"I will never forget how gentle, how kind he was with me when I was absolutely nobody in the world of football in terms of management, and how he shared his knowledge," recalls Guardiola in Sky Sports documentary El Loco and Leeds.
"We talked about football, but not just football."
The meeting is believed to have lasted over 11 hours - "they started and they could not stop," Trueba later reflected - and it certainly had a profound impact on Guardiola. He left it more convinced than ever that a move into management was his destiny, and that Bielsa's methods would form the basis of his own work in the dugout.
Less than a year later, he was put in charge of Barcelona's B team.
The rest, as they say, is history.
Guardiola would soon become known as a serial trophy winner, but Bielsa's rise to prominence had more to do with the way in which his sides played than the silverware they lifted.
The intensity and aggression of his teams was unmatched in the early years of his career. His ideas were viewed as eccentric - hence the El Loco nickname - but they proved influential.
Guardiola brought the same intensity to Barcelona after his promotion from the B team in 2008, and it has been a similar story at Bayern Munich and Manchester City. At their best, his teams, like those of Bielsa, are known to suffocate opponents when they have the ball and ruthlessly punish them when they don't.
Guardiola and Bielsa share a staunch commitment to their way of playing. It is not just about winning, but winning in a distinct style, a style supporters can identify with.
It is why, when asked for the highlight of his Leeds tenure in an interview with Sky Sports earlier this month, Bielsa did not choose their historic promotion, instead saying: "The impact of our performances on the emotions of the supporters."
Bielsa uses his playing style to excite the fanbase and he is motivated by coaxing improvement from players.
Indeed, according to Guardiola himself, the biggest lessons he took from Bielsa were human ones. His admiration for the 65-year-old is rooted in his ability to take players to new levels, to fit them into his own way of working and have a lasting impact on their careers.
"In the end, what we want is to be loved," adds Guardiola in El Loco and Leeds.
"When you go home and you get a message or a phone call [from a player], and you can feel that you gave something special to them, that is the best title. Bigger than the Champions League or the Premier League or whatever. To be loved is the most important thing. I think Marcelo has that more than any other manager."
Guardiola, Bielsa crossing paths again
There is sure to be a warm embrace when the pair meet again at Elland Road on Saturday afternoon, but it will not be the first time their paths have crossed since Guardiola's fabled pilgrimage to Argentina in 2006.
In fact, they faced each other three times as managers during the 2011/12 campaign, Guardiola's final season in charge of Barcelona and Bielsa's first at Athletic Bilbao. The first meeting of the three, on a rain-soaked night in Bilbao in November of that season, ended in a thrilling 2-2 draw which Guardiola described as an "ode to football".
"Marvellous," he beamed. "When two teams try to win, football is beautiful and the spectacle is what benefits most."
He called Bielsa's players "beasts", adding: "I have never played against such an intense team. That's why he's such a good manager - he has managed to make that team his own."
Bielsa, although frustrated to concede a stoppage-time equaliser to Lionel Messi, echoed Guardiola's sentiments. "It was lovely," he said afterwards. "I enjoyed the battles all over the pitch."
Guardiola's side were victorious in the return game in La Liga the following March, sealing a 2-0 win at the Nou Camp thanks to a first-half goal from Andres Iniesta and a penalty from Messi after the break, but their third meeting, in the Copa del Rey final two months later, was the most fateful of all.
It was Guardiola's final game in charge of Barcelona - he had already confirmed his intention to take a sabbatical - and it was therefore fitting that it came against the man who inspired him to move into the profession in the first place.
Barcelona won 3-0, two goals from Pedro and another from Messi ensuring Guardiola's glittering Barcelona tenure ended on a trophy-winning high, and it is only now, eight years later, following Leeds' long-awaited promotion to the Premier League, that fate has pitted him against Bielsa again.
It is a fascinating prospect. Leeds won promotion from the Championship playing the Bielsa way and there has been no compromise in the Premier League. After a riotous 4-3 loss to Liverpool on the opening day, they have beaten Fulham by the same scoreline and seen off Sheffield United too.
A meeting with Manchester City will not change their approach. "They are one of the biggest teams in the Premier League but we will try to play the same way we always do," said Bielsa this week. "We wouldn't know how to do it any other way."
Manchester City, meanwhile, head into the game on the back of a 5-2 loss against Leicester which revealed familiar flaws. Guardiola will be eager to put them back on track with a victory at Elland Road, but just like on that rainy night in Bilbao in 2011, he will also hope the meeting with his old mentor provides a spectacle to remember.
Watch Leeds United vs Manchester City live on Sky Sports Premier League HD from 5pm on Saturday; Kick-off 5.30pm