Lillo joined City as assistant boss in June 2020, becoming the permanent replacement for Mikel Arteta, who had taken over as manager of Sundays’ opponents Arsenal six months earlier.
Guardiola and Lillo’s friendship stretches over two decades, with Guardiola’s final playing days coming during a six-month spell at Mexican club Dorados de Sinaloa in 2006 under the management of Lillo.
Guardiola had more attractive offers at the time but with his clear desire to become a manager, he felt the opportunity to work with Lillo was too good to pass up.
And such was his impact, Lillo, who hails from Tolosa in the Basque Country, ranks alongside the great Johan Cruyff as Pep’s most significant footballing influences.
He never played the game professionally, instead he began coaching his local side aged 16 and by the age of 29 he was the youngest manager in La Liga history after winning successive promotions with Salamanca.
He has since gone on to manage the likes of Tenerife, Real Zaragoza and Real Sociedad, and has been assistant manager of the Chilean national team and at Sevilla.
And ahead of Sunday’s game at Arsenal, Guardiola has praised Lillo’s influence at City, describing him as a visionary who sees nuances in the game no-one else can.
“He is a friend of mine from a long time ago – finally we can work together,” he said. “It was a dream and is now a dream come true.
“His knowledge of the game is overwhelming. He sees some things few people in the world, me included, are not able to see.
“He makes me more calm. I am a guy who expresses my feelings too much. He makes me more calm, to read the situations better.
“I would love if he could speak better English to communicate what he sees on the pitch better with the players! But maybe he needs more time.
“He helps me a lot. Rodolfo [Borrell] too. We make a good group of backroom staff.
“I need their help, for some things I can’t see.
“That's why they are here. I need their advice and support to see things I can't.”
City are in a rich vein of form, having won 17 games on the bounce in all competitions.
Indeed, we are unbeaten in 24 matches, with our last defeat coming at Tottenham in late November.
It’s a run of results that has seen us move 10 points clear at the top of the Premier League table, qualify for the FA Cup quarter-finals and move through to our fourth-successive Carabao Cup final.
But at one stage, we were down in 12th, struggling for form and written off by many.
Guardiola says Lillo’s influence in the bad moments is one of his greatest assets as an assistant coach – and has been key to City’s revival.
“For all the managers at all the clubs, it is a challenge this season,” he said. “It’s weird for everyone.
“I am surprised that in this uncertain moment in our lives we have been consistent like we have been. I didn’t expect it, honestly.
“It’s a challenge for everyone, all around the world.
“Juanma helps me a lot to be more patient, be more calm in the bad moments. He said to me many times: ‘It’s going to change, everyone will lose games. So be calm and read what we have to do to be better.’
“That helped us. We didn't change in any game what we want to do. It doesn't matter the opponents or system we face - we try do what we have done in the last years. No more secrets than that.
“In the case of Juanma, he trained at an early age he was already in the top league in Spain. He has huge experience.”