Manchester City were poor, Barcelona did not have to play 'well' to get their two away goals.
Agüero and Dzeko looked sharp, the former taking his goal very well. Manchester City were just all over the place. They lacked belief, shape, organisation and cohesion. Barcelona really did not have to play well to beat City, which is a shame, they (Barcelona) comfortably dominated the midfield in the first half. Messi, Neymar and Suarez ran rings round the City defence with the notable exception of Zabaleta, who's only mistake was the penalty.
The tie is not over, far from it, however Manchester City face a very difficult away fixture against a side which is superior in every department.