Football is unpredictable, anything can happen. I'm not surprised about the performance of Manchester City now because I understand this is football. Their low performance might be just a little mistake, something maybe the coach is not doing it at the right way.
Why blame the coach in this case if the players have tried according to the abilities and directions of the coach himself. Because losing and winning are things that are always seen in football and yesterday's Manchester City game was pure without making any mistakes even though Manchester City had to lose at home to Manchester United. So there's no need to blame the coach in this case because all parties who are members of the team always try and want to see their team win.
No one thought Manchester united will beat Manchester city so easily today and even with the way the match started Manchester City seems to have the upper hand at first, but the second half brought the magic goal for man united.
You don't need to think about that because every team has the ability to win even though there must be a team that is at a disadvantage in the match. If you look at the statistics of possession between Manchester United and Manchester City in yesterday's match, it is clear that Manchester City is superior in that regard, but counterattacks from Manchester United always look dangerous and there are even two good chances that don't result in goals. So Manchester City must accept the fact of losing at home to Manchester United.