MANCHESTER, England — Pep Guardiola lay on his bed in a Madrid hotel room, staring at the ceiling, contemplating his next move. He had already endured two sapping games, half a dozen choleric news conferences, more than a week of highly charged, thinly veiled animosity. He was exhausted and exasperated, and he was still only halfway through.

In the space of 18 days in the spring of 2011, Guardiola’s Barcelona encountered José Mourinho’s Real Madrid four times across three competitions. There was a clásico in the Spanish league. There was a clásico in the final of the Copa del Rey. There was a pair of clásicos, home and away, in the semifinals of the Champions League.

It was not the games, though, that drove Guardiola to the sanctuary of his room. The games, if anything, were a release, a blessed respite from the endless rancor, the pervasive friction of Mourinho’s total psychological war. Guardiola knew he was being tricked into losing his cool, being sucked into a fight he could neither avoid nor win.

In retrospect, those 18 days — captured by the Italian journalist Paolo Condo in his book “The Duellists,” — were the culmination of the defining rivalry of soccer in the early years of the 21st century, a clash of cultures that reverberated well beyond the long and vituperative shared history of Real Madrid and Barcelona.

It was not just the clásico. It was not just Lionel Messi against Cristiano Ronaldo. It was not just Guardiola against Mourinho, the finest managers in the world. It was two competing visions, two contrasting styles, two opposing forces: the creator against the cynic, the light against the dark.

In the immediate aftermath, it was Guardiola who had the air of the victor. He did lose his cool, as Mourinho had hoped, and Barcelona did lose the Copa del Rey final. But Barcelona won both the league and the Champions League that year. Hindsight, though, would suggest all of that came at a cost for both men.

A year later, Mourinho finally claimed a Spanish title. It would prove to be the high-water mark of his time in Spain and the end of his decade of greatness (though he would claim a couple of championships elsewhere). Something changed in Mourinho after Real Madrid. His fire never burned as brightly.

Guardiola, too, bore the scars. He left Barcelona in 2012, drained and weary. He could not, he said, go on. He needed a break. Mourinho was not solely responsible for that fatigue, but it is hard to believe that the intensity of the rivalry was not a significant factor in it. It took Guardiola a year’s sabbatical in New York for him to refuel.

Now, more than a decade later, he could be forgiven for hearing distinct echoes of 2011. Over the next seven days, Guardiola’s latest masterpiece, the Manchester City team he has guided to three Premier League titles in four years, will face its greatest — and only — domestic challenger, Jürgen Klopp’s Liverpool, twice, across two competitions.

First, on Sunday, the teams will meet in the Premier League at the Etihad, in a game that will likely decide England’s next champion. Next Saturday, they will face off again, this time at Wembley in the semifinals of the F.A. Cup. Both matches may well prove a prelude to a third, altogether more epochal meeting: Liverpool and City are favorites to reach the Champions League final on May 28 in Paris.

The parallel with those 18 days in Spain, of course, is not perfect. Manchester City and Liverpool have fostered a fierce rivalry in recent years, but it lacks the depth and the context of the clásico. Its tendrils do not stretch back decades, nor is it bound up with questions of politics and history and, particularly, national identity.

Likewise, Guardiola and Klopp do not have the same combustible chemistry that Guardiola and Mourinho did. It would be a stretch to say they are friends, but, almost a decade after they first ran into each other in Germany, they remain cordial. In 2020, Guardiola called Klopp in the small hours of the morning to congratulate him on winning the Premier League. Klopp describes Guardiola as the best coach in the world at every opportunity.

Many of the other ingredients, though, are present. Just as with Real Madrid and Barcelona, everything rides on games between these two clubs. One of these teams will win the Premier League. One of them will go into the F.A. Cup final as the heavy favorite. Only Bayern Munich might be considered a peer in the Champions League.

Both coaches have done what they can to quash the idea, but both are perceived as chasing multiples of glory: City, a domestic and European treble, last achieved by an English team in 1999; and Liverpool, an unprecedented and, in reality, improbable sweep of all four trophies available to them. Their meetings are, in that light, the whole ballgame.

That their aims are so lofty illustrates that Liverpool and City can reasonably be regarded as the best two teams on the planet — Bayern alone may have the right to quibble with that assessment — just as Real Madrid and Barcelona could be in 2011. They are again led by the two finest coaches of their generation, the two minds who have done more than anyone else to define and distill what elite soccer will look like in the 2020s, the two scions of two great schools of thought. The rivalry of City and Liverpool does not have roots in the past. But it does encapsulate the present.

The absence of overt institutional hostility between the clubs, meanwhile, should not be mistaken for affection. The schism that runs between Manchester City and Liverpool can feel superficial, almost confected, a friction that is performed out of instinct rather than something heartfelt. But it is not.

There have been a series of flashpoints, ordinarily deemed serious transgressions by one side and dismissed as petty by the other: City’s complaint at the improper accessing of its recruitment software by Liverpool’s staff in 2013, an offense for which Liverpool paid £1 million ($1.3 million) in compensation; City’s team bus being pelted with bottles on arrival at Anfield in 2018; Liverpool’s annoyance at a 2019 video of City’s players adopting a terrace chant referring to its rival as “victims of it all,” an insult that is often associated with the Hillsborough disaster of 1989, which caused the deaths of 97 Liverpool fans.

All of these events, though, are rooted in a deep-seated clash of competing corporate philosophies. Liverpool’s hierarchy believes that Manchester City’s primacy has been achieved through a form of financial doping — as highlighted most recently by another cache of leaked documents published in Der Spiegel. Manchester City’s executives, in turn, see Liverpool as the prime example of a longstanding cartel that feels threatened by the emergence of genuine competition.

The same can be said of the coaches. Klopp and Guardiola’s mutual admiration should not make one forget the intensity of competition between them.

In a scene in “All Or Nothing,” the documentary that followed City’s victorious Premier League campaign in 2018, Guardiola and his coaching staff discuss the threat posed by Liverpool’s famed front three. That, in itself, is not especially remarkable. What stands out is that they are doing it in the changing room at Goodison Park, a few minutes before a game against Everton.

Guardiola has never made much secret of his focus on Liverpool. That same year, he told a seminar at the city’s university that he did not read many books these days, because after a few minutes of trying his mind would wander to “Jürgen Klopp and Liverpool.”

Earlier this year, with City apparently sitting on a comfortable lead at the top of the Premier League, he was asked if anyone could catch his team. Of course, he replied: Liverpool. “They are always there,” he said. “They’re a pain.” On Friday, he described Klopp as the “greatest rival” of his career.

“When I retire and I’m playing golf, I will look back on Liverpool as the hardest opponent I faced, without doubt,” Guardiola said.

For the last four years, the rivalry between Liverpool and Manchester City, between Klopp and Guardiola, has defined English soccer. The next seven days — and perhaps the next six weeks — may decide how its story is told in years to come. As Guardiola knows from personal experience, though, that level of competition leaves its mark. It is entirely possible that, when it has all come to an end, neither coach, and neither team, will quite be the same again.