Maybe we didn't need to "react" as you say - but ultimately the result suggests that the complacency wasn't justified; we lost a two goal lead! But as I said, that's just my opinion - and none of us will ever know what would have happened if we had brought the subs on straightaway!
Armchair fan here, so appreciate that others are better placed to have an opinion, but as soon as Pellegrini made his substitutions I had the feeling that they would be game changing - and minutes later I was proved right. From the time of the substitutions, and even more so after they scored...