All the billions in the world and Manchester City still cannot rid themselves of the most persistent thorn in their side. Once again, against all the odds, against all available logic, Wigan Athletic have stunned City in the FA Cup. A Wembley semi-final against Arsenal is theirs and the trophy is still theirs. The holders are still standing. How do they do it? Wigan, bloody hell.

Last year it was the final and Ben Watson's crazy last-minute winner. That was the greatest day in their history, but this was just as remarkable. This time it was a quarter-final at Fortress Etihad where no one, probably not even Wigan, truly expected lightning to strike twice. Yet goals in either half from Jordi Gómez and James Perch inspired them and then, in the face of a relentless City onslaught, they simply would not budge, throwing heart, body and soul in the way of a ball which seemed destined for their net on several occasions. For their manager, Uwe Rösler, a former City striker, it is undoubtedly the greatest result of his career.

As for City, a domestic treble is off the cards and they must haul themselves off the floor quickly with the second leg of their last-16 Champions League tie against Barcelona on Wednesday. Although they believe they can overhaul their 2-0 deficit, they cannot afford to be as lethargic as this at Camp Nou, and the time is surely approaching when Manuel Pellegrini's faith in Martín Demichelis wavers. The Argentinian remains a danger to his own team, clumsily conceding the penalty which allowed Gómez to put Wigan ahead, and it was clear that City's audibly frustrated fans do not trust him.

City can have no excuses. The visit of a Championship side would not normally send a shiver down their spine but they knew that Wigan were underdogs who would snap at their heels and that they possessed a potent bite if they were not kept on a firm leash. It is 10 months since they lost to the Latics in last season's final, something that the visiting supporters were intent on reminding everyone. That said, they could not be too afraid of Wigan given that they beat them 5-0 in the third round of the Capital One Cup in September; yet City played with the sluggishness of a side that was still recovering from beating Sunderland in the final of that competition last Sunday.

Not to take anything away from Wigan. This was an emotional afternoon for Rösler, who replaced Owen Coyle in December. The German spent four years at City in the mid-90s, named one of his sons Colin after Colin Bell and was inducted into the club's Hall of Fame by supporters. Rösler's challenge was not only to drag every last drop of sweat out of a team that was playing their 52nd match of the season because of their Europa League commitments but also not to be overcome by the emotion of the occasion.

Judging by the fearless way Wigan went about their task, there was no danger of that happening. Rösler caught City by surprise by setting Wigan up in a 5-3-2 formation that allowed them to squeeze space and dominate Yaya Touré in midfield.

For a club of City's vast resources, it is staggering that they are forced to rely on a player who always looks to be on the verge of calamity and it was hardly a surprise that Demichelis was at fault when Wigan took the lead after 28 minutes. Rolled far too easily by Marc-Antoine Fortuné, Demichelis compounded his error by standing on the striker's foot. In the absence of the injured Watson, Gómez converted the penalty.

It was happening again, but surely Wigan could not have dreamt that they would double their lead a minute into the second half. Once again, City's defending was clownish. James McArthur drove into the area on the left and pulled a low cross towards the far post, where the horribly timid Gaël Clichy allowed Perch to bundle the ball past Costel Pantilimon.

City had been woeful, their anger at their own inertia summed up when Samir Nasri received a booking for dissent, and they did not have a shot on target until the 66th minute.

However, Pellegrini, who made six changes from the win over Sunderland, responded by making three substitutions after 53 minutes and Nasri restored hope when his belting shot from the edge of the area went through the bodies and into the bottom left corner after 67 minutes. The goal stood even though Joleon Lescott was offside and arguably blocking Scott Carson's view.

Nonetheless there were 23 minutes left for Wigan to hold on and soon Micah Richards was curling a shot inches wide. Then, with 10 minutes left, Emmerson Boyce extraordinarily turned James Milner's cross over his own bar with Edin Dzeko waiting to tap home. A minute later, Carson saved from Sergio Agüero. Then, as Carson stood still, Dzeko headed wide.

Surely Wigan could not hold on. Surely City would score a second, then a third. But that's what we thought last May.

Man of the match Emmerson Boyce (Wigan Athletic)