Birmingham City suffered a defensive nightmare at St Andrew's as grateful Derby County romped to their best win under Wayne Rooney.
Blues shipped three goals inside the first 25 minutes as Rooney's Rams bounced back from losing at home to Preston on Saturday - their first defeat since the Derby caretaker boss took sole charge.
Former Blues defender Krystian Bielik cashed in on home keeper Neil Etheridge's dropped clanger in the 15th minute to volley in from close range.
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