Just three days after drawing 2-2 at Ewood Park, these two Championship clubs go head-to-head again, this time in a replay.
At the weekend, Birmingham took a surprise third minute lead in Lancashire, when Reda Khadra’s shot proved too hot for Thomas Kaminski to handle.
Nevertheless, Bradley Dack bundled home an equaliser, before Joe Rankin-Costello’s sweet strike had Blackburn in front.
However, in the first minute of stoppage time, Jordan James’ scuffed shot salvaged a replay for the Blues.
This time, there must be a winner.
Blackburn Rovers came into the tie as favourites, given that they had home advantage, and the fact they are 11 points better off in the Championship table.
Jon Dahl Tomasson’s team are currently fifth, despite only winning one of their last five league games.
Having beaten Norwich at Carrow Road in the previous round, the Riversiders will be confident of another away win here.
Birmingham City meantime have lost five successive league games, so sit 19th, a mere six points clear of danger.
The Blues overcame Forest Green Rovers in round three, so are on the cusp of round five for just the second time in 11 years.
Who will prevail at St Andrew’s?