If Chelsea didn't score Mancini would surely have brought Boyata on. In fact he was already preparing to came on until Luiz scored. Shows how much ambition Mancini has got.
I agree that Mancini is a fantastic buyer of talents. Silva, Dzeko, A.Johnson, Y.Toure, Balotelli etc are highly talented players, but his approach to the game is too negative to be a top team's manager. You might tell me that he used to be Inter's manager and had won several titles for them, but that's not important at all - Capello used to be a fantastic manager as well. At the moment, he isn't good enough for Man City. Unless they are happy with just being in the top 4.