An £88.5m spend in the summer transfer market was not supposed to presage Manchester City going down 3-2 at Cardiff City in just the second game of the Manuel Pellegrini era.

The Chilean's blueprint did not also feature having to field Javi García alongside Joleon Lescott as a makeshift central defender as he did here because of injuries to Vincent Kompany and Micah Richards. Nor did Pellegrini then expect to watch a horror show from his rearguard as Joe Hart continued last season's patchy form by flapping at the corner that allowed Fraizer Campbell to give the Bluebirds a 2-1 lead on 79 minutes.

Pablo Zabaleta was also culpable, losing Campbell for his second – from another corner – as the striker doubled both his tally, and Cardiff's advantage.

Campbell, a £600,000 acquisition last January, said: "We knew it was going to be difficult but we knew we'd get our chances. There were some great deliveries into the box and it was a great all-round team performance."

This was a fair enough analysis but the news from south Wales that Chelsea, Manchester United and the rest of City's rivals will seize on is that Pellegrini's team remain too narrow and intent on playing the slide-rule stuff through central areas that can be one-dimensional and leave them impotent.

This is all despite the £15.9m summer signing of the jet-heeled Jesús Navas, an instinctive wing-man who constantly found space squeezed via a tactic identified by Malky Mackay, the Cardiff manager.

Mackay said: "The team were incredibly disciplined and as the game grew, we grew. We knew we had the ability to counter them, but they are a very good team and if we didn't do our job properly they would punish us. We showed real character and realised that when we got on the ball we could hurt them. They had lots of possession but I thought we deserved to win the game."

In Hart, Pellegrini may have an ever-worsening headache he could do without. Ten days ago, before City's opening Premier League fixture against Newcastle United, the Chilean said of his goalkeeper: "The past is the past. Of course there is last season but we have a new season now. I hope Joe will have the performance we all know he has had in his whole career. We will see every match what will happen with him but I have a lot of trust in him. I don't worry about him.

"For me always we play the players who are giving the best performance and in the best moment. My teams does not play by name, they play by performance. For the whole team, the 22 players are exactly the same. I am not talking about anyone special."

Pellegrini was forced into this early defence of his keeper after the 26-year-old had erred two days previously when on England duty, allowing James Morrison's early shot to slip in for Scotland's opener in the friendly at Wembley.

There may be no prospect of Hart being dropped for Saturday's visit of Hull City but Pellegrini was again quizzed about his form following this defeat. Asked if he might have expected Hart to cut out the Peter Whittingham corner that Campbell headed home, the manager said: "It doesn't matter who is guilty. Defending set pieces is a duty for the whole team, not just the goalkeeper or the defenders."

With Kompany's groin injury and Richards's pulled hamstring keeping each out for up to a month, the need for a new central defender is newly concentrated following this reverse. Martín Demichelis of Atlético Madrid has been identified, though City are haggling over the Spanish club's €5m (£4.3m) valuation.

Pellegrini is insistent that this loss will not hurry the pursuit up. "I don't like to link both things," he said. "It is not the same thing. We didn't lose the match because of our centre-halves. We lost because we weren't concentrating on two corners. It was a pity. I did not expect to lose. We must continue working. We have just started and not a lot of teams will win here. They are not an easy team to play. We will try to start again when we play at home against Hull."

City should win against Steve Bruce's side. Yet they were supposed to defeat Mackay's here, too.