You had to go back to September 2018 for the last time Manchester City lost a Champions League group match at home, when Pep Guardiola was in the stands due to a ban, and Nabil Fekir’s winner gave Lyon a 2-1 victory.

Guardiola stood down all but one of the team that lost at Newcastle United and witnessed Bayer Leverkusen end a 23-match run in the type of off-colour display reminiscent of last season.

Why the manager rested so many, including Erling Haaland and Phil Foden, is intriguing considering the Newcastle reverse was on Saturday and there are four days until Leeds visit.

Kasper Hjulmand’s side prospered on the break and in space City’s leaky defence allowed, as Alejandro Grimaldo fired them into an opening period lead doubled by Patrik Schick after the break.

Beyond Guardiola’s tinkering, the wider truth is that City are no relentless winning-machine as they once were.

Guardiola offered the normal pre-game platitudes about Leverkusen being a tough opponent, then made 10 changes, with Nico González the sole man to be retained. As Hjulmand’s men arrived as the third placed Bundesliga team, eight points behind Bayern Munich, Guardiola’s thinking was understandable unless, of course, the Germans took the lead.

Then Guardiola might consider a rejig of his formation that had Tijjani Reijnders and Rico Lewis as the attacking midfield pair behind a frontline of Oscar Bobb, Omar Marmoush, and Savinho.

It was a centre-back – Nathan Aké – who went close when torching a shot at goal from a Reijnders corner on the left: Mark Flekken somehow beat the ball away from bulging the goalkeeper’s top left corner.

Alejandro Grimaldo fires Bayer Leverkusen into a surprise lead. Photograph: Peter Powell/Reuters

This outing of the many contenders to be Guardiola’s first-choice was next graced by the understudy defender Abdukodir Khusanov who skipped forward from right-back and curved the ball in for Marmoush who could not convert.

The ongoing absence of Rodri means City are too easily got at via attacks the peerless midfielder often spies and stops at infancy. So it was that Leverkusen cruised along their left, pinged the ball over, and Ernest Poku unloaded – Rayan Aït-Nouri’s sliding block was heroic and City were warned. As they were, again, when one moment Khusanov was nabbing the ball from Malik Tillman before Reijnders dawdled in Leverkusen’s area, and the visitors broke.

Fast – as, suddenly, Poku was being grappled to the ground in City’s box by Aït-Nouri, in what looked a firm case for a penalty yet while Hjulmand and his men were convinced, the referee, João Pinheiro was not.

But, now, Guardiola’s near-wholesale reshuffle of the team backfired. Once more City were caught, this time centrally, before the ball was swept right again, to Ibrahim Maza. The cross twisted the home rearguard around, Christian Kofane touched back to Alejandro Grimaldo, and the captain drove low and past James Trafford into the right corner.

Any team can concede anytime and the play to do against Guardiola’s City has always been the counter-surge. Yet since last season it has occurred far too often for his liking while there is a bluntness, too, in front of goal when Erling Haaland does not score or is on the bench as he remained at the break. Factor in, also, how Phil Foden’s paltry four goals are second to the Norwegian’s 19 and him being a replacement as well and you could see how their manager might consider introducing one or both at some juncture.

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As the temperature neared freezing, Guardiola’s role was to turn the dial up on a display which was tepid. Bobb and Reijnders each ran in and shot and each time Flekken repelled. They offered a glimmer of what was required but only that.

For the second half, Guardiola did indeed make a move. On came Nico O’Reilly for Aït-Nouri, Jérémy Doku for Bobb, and Foden for Lewis. But, it failed miserably, as Leverkusen scored again due to further iffy defending.

Alejandro Grimaldo scores the opener for Bayer Leverkusen. Photograph: Philip Bryan/Shutterstock

From the right, Maza again had copious time to spiral the ball over, Patrik Schick rose and got ahead of the dozing Aké, then directed a header beyond Trafford to the keeper’s left.

Instantly the camera moved to Haaland who, warming up, was dismayed and, after Savinho spooned over and a Foden effort went for a corner, Guardiola signalled for the striker and Rayan Cherki to strip off.

They entered on 65 minutes for Marmoush and Khusanov, cheered on as the cavalry the City faithful hoped they would prove. Instantly Haaland was rising to head at goal: he missed but you felt, at last, those in blue were potent.

Further evidence was a classic Haaland stampede forward that had Flekken diving at his feet.

City dominated the closing phase – a Cherki dribble claimed a corner but though Haaland was found he, as with his teammates all evening, could find no answer.