Birmingham secured an FA Cup fourth-round trip to Sheffield United as Wade Elliott's late goal helped beat Wolves.
The visitors had the best first-half chance of the replay at Molineux, Adam Rooney hesitating when clean through.
But a prostrate Elliott scythed in the winner from three yards after his initial effort came back off a post.
Substitute Steven Fletcher almost took the game into extra-time but his shot was smothered by Colin Doyle, who then tipped Stephen Hunt's rebound over.
Much was made of the lack of quality in the , played on a pudding of a pitch at St Andrew's 11 days ago before a sparse crowd of 14,594.
There were many empty old gold seats at Molineux and numerous changes on both sides, but Birmingham's vociferous travelling contingent ensured a lively atmosphere.
However, despite a far better playing surface the majority of the action on the field was less than inspired once again.
Led Zeppelin maestro Robert Plant flew in from Texas especially for the match but found his beloved Wolves were not in the mood for long periods.
Christophe Berra, the only Wolves player to remain from made a key interception to clear David Murphy's cross as Birmingham started positively.
Adam Hammill provided some of the better moments for the home side down the right flank, and his fine early cross was met by Sylvan Ebanks-Blake, but under pressure the burly striker headed wide from inside the six-yard box.
Hammill flashed another dangerous ball across the face of goal ahead of his team-mates, but even when Birmingham were briefly down to nine men following a clash of heads between Murphy and Jean Beausejour, Wolves could not provide a cutting edge.
Indeed it was the visitors, while still reduced to 10 men as Beausejour's treatment continued, who had the best chance of the half when Rooney raced clean through, only to take too long and allow George Elokobi to make a muscular challenge.
Curtis Davies forced Dorus De Vries into a low save to his left with a flick-on from Jordon Mutch's long free-kick, and Jonathan Spector's long-range drive from the right side fizzed inches wide of the left-hand post.
Birmingham, playing their 36th match of the season, continued to have the better of things in the early stages of the second-half, and Mutch tested De Vries with a low drive from 25 yards.
With such a lack of potency going forward, Wolves brought on their leading scorer Fletcher, who netted the opening goal at Spurs, with 20 minutes remaining.
Yet the chances continued at the other end, Beausejour's left-wing cross turned fractionally wide of his own post by Elokobi, and from the resulting corner the Blues were in front.
Elliott might have done better when he turned to meet the loose ball from close range, but his determination was evident as he forced home the rebound.
Fletcher looked set to save his team but was bravely met by Doyle as he slid in with his trademark left foot from inside the six-yard box.
Just as he had done late on in the first match, the Birmingham goalkeeper Doyle completed a fine double save, springing to his feet to keep out Hunt's volleyed follow-up, as the Blues earned a visit to Bramall Lane on 28 January.
Wolves boss Mick McCarthy: "I am very disappointed, angry, and the game hinged on us not marking from a corner so I'm disappointed with that.
"I've loads of complaints, not with them but with us for not being good enough on the night. I've said my piece in the dressing room.
"I know winning games creates that winning mentality and I didn't want to lose tonight. I'm bitterly disappointed, I didn't want to lose. I'm angry about that.
"Yes, there are a lot of changes, some enforced, some my decision, but they are all Premier League players and the best of them was Matt Doherty, the one kid on the pitch.
"I know what they can all do individually but collectively they've not done it as well as we could have done. I'm livid we've gone out."
Birmingham boss Chris Hughton: "It was a satisfying result. Wolves made more changes than us but to come here and win was excellent.
"We had to defend very well at times and our two centre-halves Curtis Davies and Steven Caldwell were excellent and we needed them.
"But I thought we showed enough on the ball to be a real threat at times and in the end we just deserved it."