Just to put the result into some perspective, Birmingham's results in the runup to the match were as follows
December 26 (h) L Nottingham Forest 0-1
December 28 (a) D Manchester City 1-1
January 1 (a) L Manchester United 0-1
January 11 (h) L Ipswich Town 0-1
After the tie they lost again to Everton before finally winning against Oxford United (who only finished 3 points below City) on February 1st. On the night, they had David "Seasman" and Julian Dicks (his actual name!) in the team. So they were poor but not hopeless. Though it was not long until they were in division three.
The crowd that night of 6,636 was only a few hundred more than the famous Frickley-Rotherham tie in the same round - Frickley finished second that season.