Jerome bundled the ball past Hennessey for the opening goal
Birmingham defeated Championship leaders Wolves to close the gap at the top of the table to just two points after a dramatic West Midlands derby at St Andrew's.
Blues skipper Lee Carsley was sent off in the first half for an horrendous studs-up challenge on Chris Iwelumo, who was stretchered from the field.
But Cameron Jerome somehow bundled the ball home close to the break to put 10-man Blues ahead after the Wolves defence made a complete hash of clearing a seemingly innocuous free-kick.
Birmingham came close to a second when Wayne Hennessey denied Lee Bowyer but Garry O'Connor did double their advantage, coolly slotting home from a tight angle after skipping past the Wolves keeper.
The result extended the the home side's unbeaten run to six games and sets up an intriguing conclusion to the season as the Midlands rivals both push for promotion, while Reading and Sheffield United remain in joint-third place, six points adrift of Birmingham.
Wolves could have extended their lead over Blues to eight points and taken a huge step towards achieving their goal of a return to the Premier League.
But Mick McCarthy's team were second best for most of what was a scrappy and uncompromising encounter and were particularly disappointing after Carsley's dismissal gave them a numerical advantage.
Birmingham, in contrast, closed down their opponents with a gritty determination and enjoyed the bulk of the contest's clear-cut openings.
Wolves started reasonably well and created most of the few openings of note during a frenetic opening phase to the game in which errant passes and crunching tackles held sway over attractive football.
Dave Edwards shot wide under pressure and narrowly missed with a header from Stephen Ward's cross, while Dave Jones curled a free-kick over the wall but Maik Taylor comfortably saved.
Birmingham had looked ineffectual in attack but a near disastrous backpass from Ward gifted Jerome the game's first clear-cut chance.
Stephen Carr can take huge credit for his role in creating the opening as he pressurised Ward into trying to find his keeper from the half-way line.
Jerome latched on to the ball and closed down on goal but his attempt was smothered by advancing keeper Wayne Hennessey while the striker subsequently failed to hit the target from 20 yards with the rebound.
O'Connor made sure Birmingham go two points behind Wolves
Sebastian Larsson was inches away with a brilliant free-kick as the momentum swung towards the home side and Kevin Phillips looked set for a run at goal after beating the offside trap but a heavy first touch saw the chance got to waste.
Then came the game's first significant moment as Blues midfield lynchpin Carsley was correctly dismissed for his scything challenge on Iwelumo.
The Birmingham skipper trudged off inconsolably - but shortly afterwards his team were in front to a goal of almost indescribable scrappiness.
The visitors failed to clear a free-kick that was flicked on by Radhi Jaidi and Jerome somehow managed to bundle home despite being surrounded by a phalanx of Wolves players while keeper Hennessey had one hand on the ball.
Wolves brought on winger Matt Jarvis for full-back Matt Hill as they tried to prise their way back into the contest, but the match continued in the same disjointed manner that characterised most of the opening 45 minutes. Defensive hesitancy almost cost Wolves again as a long ball forward was allowed to bounce and there was precious little evidence of their numerical advantage.
Wolves boss McCarthy implored his team to push forward but it was without effect and it was the hosts who looked most likely to score the game's second goal, with Hennessey denying Bowyer and Larsson shooting wide.
Birmingham did eventually strike again when second-half substitute O'Connor collected a ball over the top, evaded the dive of the advancing Hennessey and slotted home with great composure.
Liam Ridgewell might have added a third with a header from a corner that Hennessey saved as Blues reinvigorated their title challenge.
Birmingham manager Alex McLeish:
"Big win, we gave a terrific performance tonight, one of the best of the season at St Andrew's.
"I know we could have played better at times this season, but we have hung in there and showed some great resilience and steel throughout the team.
"The team have persevered, the never say die spirit is there and what we have lacked in skill sometimes we have shown in energy and spirit."
On Lee Carsley's sending-off: "From where I was I thought Lee wasn't favourite for the challenge. The ball is there and I think he has gone genuinely for the ball.
"He's not a dirty player. He's very hard but fair and I think he's gutted that the lad is injured."
Wolves manager Mick McCarthy:
"I'm disappointed. There was lots of incidents in the game and not too many I'm pleased with to be honest.
"If I start about the referee's performance I will be here until 12 o'clock tonight, so quite clearly I'm not pleased about that.
"If we had been offered five games to go and two points clear of second and eight clear of third and fourth, we would have taken it. We would have been delighted.
"Giving a team who has got a good defensive record something to hold onto, I thought they did it very well and caught us on the break, so they have done well."
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