A goal in each half from Birmingham old boy David Dunn secured Blackburn a deserved win over Alex McLeish's side.
Dunn crashed a fifth-minute shot past Joe Hart after Birmingham failed to clear Christopher Samba's clearance.
Early in the second half Birmingham equalised through a superb James McFadden left-footed free-kick.
But Birmingham never got to grips with Rovers' adept use of set-pieces and it was Dunn again who used his strength to head a near-post corner past Hart.
Dunn, who rejoined Rovers in 2007 after spending three-and-a-half years with Birmingham, had a fine game for Blackburn, allying skill with the ability to fight his corner.
Allardyce annoyed Dunn denied hat-trick
If his first goal demonstrated exemplary technique in how to strike the ball, his second was all about determination as he outmuscled Stephen Carr to reach an El-Hadji Diouf corner.
During the first half Dunn lashed another shot past Hart but the goal was disallowed after Michel Salgado was penalised for a foul in the build-up.
Dunn's career has been blighted by injury - and he limped off late in the second half after a kick from behind by Barry Ferguson - but this was a performance that highlighted what a talented player he is.
In between his goals Dunn was a constant menace to Birmingham and just before the interval his clever pass - signalling with his eyes that he was going to go right, before delivering the ball to his left - allowed Diouf the opportunity to cross.
Hart was unable to gather the ball cleanly and needed Liam Ridgewell to clear for a corner, with Morten Gamst Pedersen lurking.
Birmingham were constantly unsettled by the home side's physical presence from set-pieces - no better illustrated than by the way Dunn nabbed that second goal - with Hart frequently needing to punch the ball clear.
With Blackburn getting the ball forward as quickly as possible, Birmingham preferred a more patient approach.
It was the visitors who put together the first-half's most stylish move, which ended with Carr testing Blackburn keeper Jason Brown with a dangerous low cross.
McLeish lays down player challenge
Soon after Dunn's first goal, Brown had to show equally swift reactions to turn away a dipping McFadden shot.
But the Blackburn goalkeeper could only watch on 55 minutes as McFadden's left-footed free-kick swung round the Rovers wall to find the corner of the net to pull Birmingham level.
Dunn struck again 12 minutes later but in the fifth-minute of stoppage time Blackburn had a narrow escape.
Samba's pass to Brown was too short, but Rovers managed to scramble the ball clear to hold on for a win that all but guarantees their Premier League survival.
Blackburn manager Sam Allardyce: "I'm proud to say we are in the top four of the Premier League with home results.
"It's been a great performance. David Dunn turned the game in our favour and it was a shame he was denied a hat-trick - there was nothing wrong with that goal that was ruled out in the first-half.
"We must remember we have some terrific young players who have made massive contributions. Steven N'Zonzi is my player of the season. He's played every Premier League match. He is a major find."
Birmingham boss Alex McLeish: "We totally dominated. I thought there was only going to be one winner after James (McFadden) equalised.
"We shipped in a soft goal but what annoyed me about it was the foul on Roger Johnson for the flick on that lead to the corner.
"Samba climbed all over the top of him and how can the referee not see that?"
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