To be fair to City, there seemed to be a combination of many things last night that put a bit of a dampener on things ... the aftermath and tiredness (physical and mental) after losing at Anfield, not having either of our real game-changers / best passers (Silva & Toure) on the pitch, a strangely quiet and low-key crowd / atmosphere, Sergio not being back to his best and labouring up-front, Negredo's total loss of confidence in front of goal, Martin Atkinson in charge after we'd just had Clattenburg, etc, etc. The Liverpool result seemed to have deflated the crowd too.
I sensed some of these things even before the game started, and I think Sunderland did too - and it encouraged them as they really looked all night asthough they thought they could/would win, something they just haven't looked like doing for the past 7 or 8 weeks.
And we should also acknowledge that if Kompany hadn't mis-kicked at Anfield, and Nasri had finished his fairly simple chance last night (both of which would have gone right 9 times out of 10), then we'd have virtually won the title already ... so it really is quite fine margins between success and despair.