Birmingham, who have now gone 13 games without a win, went behind to a fine individual goal by Julian Joachim after nine minutes. Ian Ormondroyd added a second 20 minutes later and Iwan Roberts completed the scoring.
John Aldridge revived Tranmere Rovers' promotion ambitions with both goals in a 2-0 home win over Stoke City.
Plymouth Argyle went top of the Second Division, beating Rotherham United with three goals in the last 14 minutes. Reading, who had led the table since November, drew 1-1 at home to Bradford City. Lee Power, Bradford's recent signing from Norwich, scored Bradford's equaliser.
The Third Division also has new leaders, Dave Thompson's winner against Walsall sending Chester City ahead of Crewe Alexandra, who lost 2-1 at Scunthorpe United.Reuse content