im currently managing man city aswell, the tactic you are using sounds good, but when you are playing them away maybe change your mentality to defensive and counter attack on seeing as your playing chelsea they will come at you, and you can just catch them on the CA. another thing that might work is if you get a lead change your time wasting to often that way your team wastes as much time as possible and your passing to short that way you make quick little passes which will tire the opponents out. thats what i did my first game against a big club and it worked. so give it a try and i hope i gave you atleast sometype of idea on what to do