Chelsea's equaliser came in a very simple manner.
Juan Manuel Mata played a good ball out to the wing for Branislav Ivanovic to collect and cross. The cross was pinpoint, and Daniel Sturridge's header was superbly placed into the net.
Throughout the entirety of the first half and most of the second, Chelsea omitted the wide areas of the pitch and found no joy through the middle.
Chelsea were simply camping outside Birmingham's box, and no matter how many times Raul Meireles tries to play the perfect, curling ball into the box, the Blues were unable to create any chances.
On the occasion they did use the width, they fashioned a chance or two. It's odd that it took Chelsea 60 minutes to realise this was their best chance at success.