The two clubs are currently enduring contrasting seasons, with Rovers sitting in fourth in the standings and Blues just six points above the relegation zone.
Match preview
After 27 matches without a Championship draw, that moment finally arrived for Blackburn last weekend as they earned a share of the spoils at Bristol City, holding on for a 1-1 draw while being at a player disadvantage for the final 16 minutes.
With three defeats having come in their previous four league games, Jon Dahl Tomasson would have felt grateful for a point, particularly against one of the improving teams in the division.
The result was also enough to keep Rovers in fourth position, even though they can effectively rule out a bid for the top two now with Sheffield United 14 points clear.
With Blackburn having no history when it comes to reacting to stalemates under Tomasson, it remains to be seen how they will fare on Saturday, but they can take confidence from their performance in the previous round.
A first-half Jack Vale proved to be enough to see off Norwich City at Carrow Road, and Tomasson will now sense an opportunity to go deeper in this competition.
Birmingham, on the other hand, will view this occasion as a welcome distraction from the Championship after losing five consecutive matches.
Blues have quickly gone from dark horses for promotion to finding themselves bidding to remain out of a relegation battle, the gap currently at six points at a time when teams below them are improving.
With issues behind the scenes a constant topic for conversation, John Eustace knows that the club as a whole require something to cheer on the pitch.
Birmingham came from behind to defeat Forest Green Rovers in the third round, Lukas Jutkiewicz and new signing Kevin Long scoring the goals in a 2-1 triumph over the League One strugglers.
Blackburn Rovers FA Cup form:
W
Blackburn Rovers form (all competitions):
L
L
W
W
L
D
Birmingham City FA Cup form:
W
Birmingham City form (all competitions):
L
L
L
L
W
L
Team News
Hayden Carter is expected to be given an opportunity in the Blackburn defence with Daniel Ayala serving a one-match suspension.
Second-choice Aynsley Pears could also be given a run out, as could the likes of Lewis Travis and Tyrhys Dolan.
However, having had no midweek game, Tomasson may be prepared to name a more familiar side than usual in the cup.
Eustace must decide whether to stick with the 4-4-2 formation which proved unsuccessful versus Preston North End last weekend or revert to a back three.
Either way, alterations will be made in personnel with Juninho Bacuna and Jutkiewicz among those who are pushing for a starting role.
Goalkeeper Neil Etheridge, who made headlines with an astonishing triple save in the previous round, is also in line to start between the sticks.
Blackburn Rovers possible starting lineup:
Pears; Rankin-Costello, Carter, Wharton, Pickering, Buckley, Morton; Hedges, Dolan, Brereton Diaz; Vale
Birmingham City possible starting lineup:
Etheridge; Colin, Long, Friend, Trusty; Chong, Bacuna, Bielik, Khadra; Deeney, Jutkiewicz
We say: Blackburn Rovers 2-0 Birmingham City
While Blues boosted their confidence with a win over Forest Green in the previous round, we cannot ignore their form at the second tier. Although Blackburn have been far from perfect themselves, they should have enough quality in their ranks to record a relatively comfortable win.