Premier League outfit Wolves struggled to gain the upper hand against their Midlands rivals from the Championship before a sparsely populated St Andrews.
Wolves could have snatched victory in the last minute of injury time only to be denied by a superb double save from Birmingham goalkeeper Colin Doyle.
Doyle tipped a curling Matt Jarvis shot onto the post and then parried away Steven Fletcher's follow-up shot on the rebound as Birmingham clung on for a replay.
Liverpool had got the third round under way on Friday with a 5-1 victory over Oldham at Anfield.
In other matches on Saturday, League Two Cheltenham travel to high-flying Tottenham dreaming of an upset while non-league Tamworth head to Goodison Park to face Everton.
The pick of the third round ties falls on Sunday, when holders Manchester City take on bitter rivals Manchester United at Eastlands, with Arsenal entertaining Leeds on Monday.