It was a night when Pep Guardiola twisted on the tactical front and then twisted some more. For plenty of a slow-burning encounter, a part of the battle was to decode the schemes of the Manchester City manager. And when he twisted yet again on the hour, he got what he wanted – a lovely team goal, finished off by Riyad Mahrez, to cut the gap to Arsenal at the top of the Premier League table to five points. Guardiola had introduced Mahrez on the right and Jack Grealish on the left – a double substitution that highlighted the riches at his disposal – and, within three minutes, the pair had combined at the end of a right to left and back to the right move, which also featured Kevin De Bruyne. When Grealish crossed, Kepa Arrizabalaga chose not to throw out a hand – a weird decision – and Mahrez did the rest, deepening the sense of introspection at Chelsea in the process. They have now taken just six points from an available 24. It was the main event before Sunday’s FA Cup third-round meeting at the Etihad Stadium and the stakes were high for both teams, the pressure intense. City had already shooed Chelsea out of the Carabao Cup but nobody was thinking about that. Or indeed, the next cup tie. Graham Potter, who was without Mason Mount because of a training ground knock, would lose Raheem Sterling after just two minutes. The manager says that nobody wants to hear excuses but his ever-lengthening injury list does feel like one. It would get even worse when Christian Pulisic was forced off before the 20-minute mark, pushing the number of stricken Chelsea players into double figures. Pulisic was hurt after John Stones stretched into a saving block challenge on him. The winger was in after a nice Kai Havertz pass but Stones slammed the door shut. Chelsea had broken after a mix-up between Kyle Walker and João Cancelo. City were smarting from the Everton game, Guardiola’s selection a statement of intent, Walker, Cancelo, Ilkay Gündogan and Phil Foden all back. And what about the system? It was enterprising, attacking and a little hard to read at first, perhaps even for the City players. Guardiola started Walker on the right of a back three, Cancelo high up on the right, Foden the same on the left. It felt as though Rodri was the only vaguely fixed point in an extremely fluid midfield. Then again, he sometimes dropped into the defensive line. Potter has not pulled his punches about his team’s travails. Chelsea kicked off not only as the fifth-placed team from the capital but the third from west London – behind Fulham and Brentford. But they were bright in the first half, winning the duels, bringing the intensity. Mateo Kovacic and Denis Zakaria caught the eye in midfield; Havertz drifted into dangerous spaces. City needed a Bernardo Silva tackle to snuff out the substitute Carney Chukwuemeka after a Havertz pull back. And it was Chukwuemeka who so nearly broke the deadlock just before the interval. Following another Havertz pass, he cut inside from the right and watched his shot beat Ederson, via a slight deflection, and rebound off the post. It was strange to see City so disjointed in the first half. And yet when Erling Haaland is around, no defender can ever relax. Out of very little on 38 minutes, he crackled to life, taking a Gündogan pass with a fabulous first touch, veering away from Kalidou Koulibaly and unloading the shot in what felt like the same pre-programmed movement. The backlift was minimal to give Koulibaly less chance to get across, Arrizabalaga less time to react. It whistled narrowly over. Guardiola was not happy at half-time and he hooked Walker and Cancelo. On came Rico Lewis and Manuel Akanji. Lewis tucked in alongside Rodri when City had the ball – the formation was best classified as 3-2-4-1 – while he covered at right-back out of possession. Bernardo went wide right. City improved. They squeezed higher, they came to find their pass-and-move grooves. Nathan Aké headed against the crossbar from a De Bruyne cross after a short corner routine while Bernardo Silva beat the unconvincing Marc Cucurella to pull back for De Bruyne who blasted wide. Thiago Silva had lashed wide at the other end but it felt as though a City breakthrough was coming. They came to enjoy greater time on the ball. They started to get in around the sides. Guardiola’s introduction of Mahrez and Grealish on the flanks would yield the richest of dividends. It was over to Chelsea to react and Potter chose the withdraw the ineffective Pierre-Emerick Aubameyang, who had earlier come on for Sterling, as one of his changes. Aubameyang was not impressed. Nor was Hakim Ziyech, who also came off. City, though, continued to threaten on the counter, with Haaland stretching and narrowly failing to convert a De Bruyne cross.