It was in the past that we do use past record to predict the future, but this season proved everyone wrong that past history doesn't guarantee future results. I see Chelsea as the favorite in this match, because City have lost form and are unpredictable when playing with big clubs. Imagine how they lost their only chance of qualifying to the round of 16 to PSG, despite on two goals lead.
Literally it's not that we completely depend on the past to make out predictions, basically it's supposed to be that the past was to give us a insight of a possible outcome when certain teams meet and not an absolute to an expectation from both teams, but some persons makes it the absolute and. That could be reason for some of their losses this season. Chelsea has got a very fierce record with Manchester city of which entails mostly an epic game between the two sides , so for fixtures like this expectations usually are kept at its minimal.