City had struggled before the break at Stamford Bridge, unable to exert their usual control and lucky not to fall behind when Carney Chukwuemeka struck the post. But Guardiola's substitutions, and one of them in particular, proved pivotal in the 1-0 win.

Lewis, a beaming Guardiola said in his post-match press conference, "changed the game" after replacing Kyle Walker, the academy product ostensibly lining up at right-back but, as in his previous appearances, spending most of his time in central midfield.

There, in an area of the pitch Chelsea had previously dominated, Lewis' short, sharp passing and intelligent positioning allowed City wrestle back the initiative, at the same time as giving his team-mates the platform they needed to find their groove.

The decisive goal, created and scored by fellow substitutes Jack Grealish and Riyad Mahrez, came from City's left flank. But by the end, a far bigger proportion of City attacks had come down the opposite side, where Lewis was operating. It was no coincidence.

• Man City transfer rumours: Lewis to get new contract?
• Pep: Lewis changed the game | 'He makes everyone better'
• Carra on Man City goal: Cucurella didn't defend

"There are players who play for themselves really well, but he has the ability to make all the team play better," added Guardiola. "He has this ability and it's not easy to find it. He is our little Philipp Lahm."

It was of course with Lahm at Bayern Munich that Guardiola awoke to the possibility of instructing a full-back to tuck inside, something which has subsequently become a feature of his approach.

Lahm's "metamorphosis", as it is termed by author Marti Perarnau in his book Pep Confidential, began with a suggestion from Guardiola's former assistant Domenec Torrent during Bayern's European Super Cup meeting with Chelsea in 2013.

"Why don't we try Lahm as a pivote?" Torrent asked Guardiola as they watched Jose Mourinho's side exploit the space behind Toni Kroos that night at the Eden Arena in Prague.

So they did, the mid-game adjustment helping Bayern come from behind to draw 2-2 in extra-time before winning the game in a penalty shoot-out and lifting the trophy.

"If we win anything this season, it will be thanks to that decision to move Lahm," Guardiola reflected afterwards. "All the other pieces fell into place the minute we put him in central midfield."

Bayern went on to clinch the first of three consecutive Bundesliga titles with Lahm operating centrally, their success providing a template Guardiola would later take with him to City.

Looking back, the similarity between Guardiola's praise for Lahm and that which he is now giving Lewis is striking. On Lahm: "He is super-intelligent, understands the game brilliantly, and knows when to come inside or to stay wide." On Lewis: "He is so clever, so intelligent. Every moment, he knows when to open inside, and what to do."

Those comments came nine years apart, but Guardiola could easily be talking about the same player.

What is most exciting for City, of course, is that while Lahm learned the role as a Champions League-winning full-back aged 29, Lewis is doing it having only turned 18 in November, as if tailormade in City's academy for this precise function. He was not even born when Lahm broke into the Bayern Munich first team.

It is impossible not to get excited about what he could become.

"I think he's going to be a superstar," Micah Richards, a former City prodigy himself, said on Sky Sports after the teenager's eye-catching display against Liverpool in the Carabao Cup last month.

"I rarely put that pressure on players because I don't think it's nice, and if they don't make it to that level, they say they're overhyped - but this is a special player that we're seeing."

Richards' struggles with injury are of course a reminder of the obstacles that can arise in even the most promising careers, but Lewis' breakthrough could hardly offer more encouragement.

His performance against Chelsea was, after all, merely a continuation of what came before it. Across his six Premier League appearances, he has a pass success rate of 93 per cent, putting him behind only John Stones and Manuel Akanji among City players - and that despite playing in areas of the pitch where he faces considerably more pressure from opponents.

The first five starts of his senior career have required considerable steel for someone so young, coming against Sevilla, Chelsea, Liverpool, Leeds and Everton, and yet he has sailed through them.

It is in midfield that he has most delighted his manager, finding space then using it to recycle possession quickly and efficiently, but Lewis has the qualities of an orthodox full-back too.

He is quick and combative, his physical attributes and mental toughness developed during a childhood spent training in his father's Thai boxing gym as well as in City's academy, and he is just as comfortable hugging the touchline as he is tucking inside.

Indeed, his goal against Sevilla in November, a goal which made him the youngest player to score on his first Champions League start at 17 years and 346 days old, came from precisely that position, Lewis collecting a Julian Alvarez pass then drilling a diagonal finish beyond Sevilla goalkeeper, and World Cup hero, Yassine Bounou.

Guardiola was quick to point out after that game that Lewis was not gifted his opportunity - "we don't give presents because he is a Man City fan or from the academy" - instead revealing he had been marvelling at the teenager's ability since "day one" of pre-season.

"This guy has something special," Guardiola added that night.

It is an assessment which rings even truer two months later.