It's mainly down to a fundamental lack of performance from their key players. We need to avoid deluding ourselves into thinking Chelsea are a poor side, they're a very good side on an appallingly bad run of results. Players who last season, and in some cases for seasons before, have been quality performers, are making mistakes, or having zero impact on the game. Hazard, Costa, Ivanovic, Terry, Fabregas, these aren't poor players, but to see them so far this season, you'd wonder how they have Premier League winners medals. They'll start to come good eventually (at least in the main, there's age concerns around Terry and Ivanovic at this stage) but, thankfully for City, we've already got an 11 points lead on them. If, between now and the end of the season Chelsea pick up 11 points, or more, on City then I'd be stunned.