They squandered their two goal lead because United dominated the match. More balance in the formation and energy.
Manchester United did not dominate the match. They had more possesion in the first half, but did very little with that possession. Manchester City scored two goals - one from awful goalkeeping and poor defending and one from awful goalkeeping.
Second half you obviously changed it around and Mancini reacted like a dazed whale after one too many pints of penguin broth. Bringing Barry on was the correct idea - but far, far too late.
Your first was a well worked goal. The Nani goal was taken well but was piss poor defending and the third again was piss poor defending.
The defending on show from both sides was pretty woeful for large chunks of time. Not sure what's wrong with Ferdinand - but he looked off the pace and Vidic looked a stranger - I'm guessing from their body langauge they don't trust your new keeper at all.
The biggest and strangest decision from Manchester City and Mancini was after establishing that the new Manchester United keeper was unlikely to ever save a long range shot - they stopped their long range shooting.
Was a game of poor tactical ambition from both managers - but Manchester United used the benefit of several key decisions (The main one being Evra remaining on the pitch after cynically fouling as last man back).
First half was abysmal from both sides - not a good game to watch by any stretch of the imagination. Second half was a game littered with mistakes and poor tackles and terrible officiating.
Not one to write home about despite the scoreline.