Sone Aluko scored twice against his former club to help Hull see off Birmingham in a pulsating encounter.
Aluko ran clear twice to put the Tigers in command inside 30 minutes and James Chester headed home the Nigerian's corner to make it 3-0 soon after.
Ravel Morrison replied for Blues when he met Nikola Zigic's knockdown.
Zigic's header set up Marlon King to pull another goal back at the start of the second half but Hull held out and remain fourth in the Championship.
Aluko, 23, came through the ranks at Birmingham and spent more than 10 years at his boyhood club before leaving in 2008.
He was making his first return to St Andrew's, and quickly made an impact.
Aluko beat the offside trap for the first time after only six minutes but saw his shot blocked by Birmingham keeper Jack Butland.
The home side did not learn their lesson, however, and Aluko soon escaped again - this time rounding Butland to score.
Birmingham's defence continued to keep a high line up the field and Aluko took full advantage to add his second goal after 26 minutes.
Hull keeper Ben Amos was called into action for the first time when he saved at the feet of Zigic but things got worse for the home side when Chester met Aluko's inswinging corner to make it 3-0.
Only then did Birmingham find a response, with Morrison scoring his first goal since joining on loan from West Ham in August, and Tigers defender Abdoulaye Faye lucky not to then give away a penalty for handball.
The fightback gathered more momentum when Blues scored their second goal just 21 seconds after the break, but Hull denied them any more clear-cut chances.
In fact the Tigers had opportunities to make the game safe, with Stephen Quinn dragging a shot wide and substitute Aaron Mclean heading over.
And Hull boss Steve Bruce, a former Birmingham player and manager, was able to celebrate his side's first win at St Andrew's since 1970 and only their second victory there in more than 100 years.
Birmingham assistant manager Terry McDermott:
"We are all devastated. The only thing to be pleased about was showing some character to come back with two goals.
"If you don't win your home games you are not going to be in the play-offs. We know what is wrong and we will put it right.
"You should not have to score four goals at home to win. But while we collapsed against Barnsley I thought against Hull we could have got back into the game."
Hull manager Steve Bruce:
"It was an unbelievable turnaround. But credit to Birmingham they stuck at their task just when I thought the crowd would turn against them. They played their part. Birmingham kept flying the ball into big (Nikola) Zigic and that is the best I've seen him play.
"The team talk at half-time was to keep it tight and they scored again after 12 seconds. It just shows what rubbish you talk.
"But I thought some of our football in the first half was very good. I have some really good players and the way Aluko is playing is there a better player in the Championship? He has been excellent for us."
Live Text Commentary
The ball is delivered by Mitch Hancox.90:00 +2:27 Booking
Booking David Meyler goes into the book.90:00 +1:33
The referee blows for offside. Jack Butland takes the indirect free kick.89:34
Jonathan Spector delivers the ball. A cross is delivered by Mitch Hancox, Alex Bruce makes a clearance.89:24
The ball is delivered by Ravel Morrison, clearance made by Alex Bruce.89:15 Full time
Full Time The final whistle is blown by the referee.88:42 Booking
Booking The referee shows Hayden Mullins a yellow card.88:40
Hayden Mullins concedes a free kick for a foul on Stephen Quinn. David Meyler takes the free kick.87:57
Foul by Mitch Hancox on Sone Aluko, free kick awarded. Ahmed Elmohamady takes the direct free kick.87:05
Effort on goal by Aaron Mclean from inside the area goes harmlessly over the bar.86:42
The ball is swung over by Mitch Hancox, Alex Bruce makes a clearance.86:17
David Meyler crosses the ball, save by Jack Butland.84:46 Substitution
Substitution Mitch Hancox on for David Murphy.84:06
Hayden Mullins crosses the ball, save by Ben Amos.83:05
Aaron Mclean concedes a free kick for a foul on Paul Robinson. Jack Butland restarts play with the free kick.81:16
Aaron Mclean has a header from close in and clears the crossbar.79:43
Outswinging corner taken right-footed by Christopher Burke, clearance made by James Chester.79:19
Jonathan Spector delivers the ball, Ahmed Elmohamady makes a clearance.79:07
The ball is swung over by David Murphy, Abdoulaye Faye makes a clearance.77:14
The referee blows for offside. Free kick taken by Ben Amos.
Inswinging corner taken by Nathan Redmond from the left by-line, clearance by Alex Bruce.74:51
Direct free kick taken by Abdoulaye Faye.74:51 Substitution
Substitution Aaron Mclean joins the action as a substitute, replacing Jay Simpson.74:51
Free kick awarded for a foul by Paul Robinson on Jay Simpson.74:18
Corner taken right-footed by Nathan Redmond from the left by-line, clearance by Alex Bruce.73:00
The ball is sent over by David Murphy.71:28
Abdoulaye Faye gives away a free kick for an unfair challenge on Nikola Zigic. Ravel Morrison restarts play with the free kick.69:04 Substitution
Substitution Robbie Brady comes on in place of Liam Rosenior.66:43
David Meyler sends in a cross, Steven Caldwell manages to make a clearance.65:24
David Meyler fouled by Nikola Zigic, the ref awards a free kick. Direct free kick taken by Ben Amos.64:37
Indirect free kick taken by Jack Butland.64:37 Substitution
Substitution Wade Elliott leaves the field to be replaced by Nathan Redmond.64:37
The referee blows for offside.64:02
Nikola Zigic concedes a free kick for a foul on David Meyler. Direct free kick taken by David Meyler.62:31 Substitution
Substitution David Meyler on for Seyi Olofinjana.61:16
The ball is crossed by Jonathan Spector.59:08
The ball is delivered by Ahmed Elmohamady, clearance by Jonathan Spector. Corner taken by Robert Koren from the left by-line, Shot from inside the six-yard box by Jay Simpson goes wide right of the goal.57:03
Sone Aluko crosses the ball in from the free kick.57:03 Booking
Booking Nikola Zigic receives a yellow card.56:53
Foul by Wade Elliott on Ahmed Elmohamady, free kick awarded.54:23
Christopher Burke takes a outswinging corner from the right by-line to the near post, clearance made by Ahmed Elmohamady.54:00
David Murphy fouled by Sone Aluko, the ref awards a free kick. Direct free kick taken by David Murphy.52:46
Stephen Quinn produces a left-footed shot from just outside the box that goes wide right of the goal.50:18
A cross is delivered by Jonathan Spector, James Chester makes a clearance. The ball is swung over by Jonathan Spector. Nikola Zigic challenges Ahmed Elmohamady unfairly and gives away a free kick. Ben Amos takes the direct free kick.49:33
The ball is crossed by Stephen Quinn, Jonathan Spector manages to make a clearance.48:17
Robert Koren produces a right-footed shot from long range which goes wide right of the target.45:21
Assist by Nikola Zigic.45:21 Goal scored
Goal! - Marlon King - Birmingham 2 - 3 Hull Marlon King gets on the score sheet with a goal from just inside the penalty area to the bottom right corner of the goal. Birmingham 2-3 Hull.45:01
The referee gets the second half underway.45:00 +3:03 Half time
Half Time The first half comes to an end.45:00 +1:45
Shot by Ravel Morrison from a long way out goes over the net.45:00 +0:22
Jonathan Spector gives away a free kick for an unfair challenge on Sone Aluko. Robert Koren crosses the ball from the free kick right-footed from left by-line, Jonathan Spector manages to make a clearance.43:02
Christopher Burke decides to take the corner short. A cross is delivered by Christopher Burke, Alex Bruce manages to make a clearance. Christopher Burke crosses the ball, Alex Bruce manages to make a clearance. James Chester challenges Nikola Zigic unfairly and gives away a free kick. Wade Elliott takes the direct free kick. Marlon King takes a shot. Blocked by Alex Bruce.41:50
Wade Elliott sends in a cross, clearance made by Alex Bruce.41:17
Outswinging corner taken from the right by-line by Christopher Burke, clearance by Alex Bruce.41:05
The ball is delivered by Marlon King, James Chester manages to make a clearance.40:25
Jonathan Spector delivers the ball, clearance made by Alex Bruce.38:59
A cross is delivered by Christopher Burke, James Chester manages to make a clearance.37:54
Nikola Zigic provided the assist for the goal.37:54 Goal scored
Goal! - Ravel Morrison - Birmingham 1 - 3 Hull Ravel Morrison grabs a goal from inside the penalty box to the bottom right corner of the goal. Birmingham 1-3 Hull.37:44
The ball is crossed by Jonathan Spector.34:14
Foul by Ahmed Elmohamady on Paul Robinson, free kick awarded. Jack Butland takes the free kick.33:35
Foul by Nikola Zigic on Stephen Quinn, free kick awarded. Ben Amos takes the direct free kick.32:21
Assist by Sone Aluko.32:21 Goal scored
Goal! - James Chester - Birmingham 0 - 3 Hull James Chester scores a headed goal from inside the six-yard box. Birmingham 0-3 Hull.32:10
Corner taken by Sone Aluko from the right by-line,29:46
Ravel Morrison challenges Stephen Quinn unfairly and gives away a free kick. Ben Amos restarts play with the free kick.27:10
The ball is crossed by Liam Rosenior, clearance made by Paul Robinson.25:50
The assist for the goal came from Jay Simpson.25:50 Goal scored
Goal! - Sone Aluko - Birmingham 0 - 2 Hull A goal is scored by Sone Aluko from inside the box to the bottom right corner of the goal. Birmingham 0-2 Hull.24:59
The ball is delivered by David Murphy. Free kick awarded for an unfair challenge on Steven Caldwell by Jay Simpson. Steven Caldwell restarts play with the free kick.22:21
A cross is delivered by Wade Elliott, Steven Caldwell takes a shot. Ben Amos makes a save.22:10
Wade Elliott takes a inswinging corner.20:46
David Murphy crosses the ball, Nikola Zigic produces a header from inside the area that goes over the crossbar.16:22
Christopher Burke delivers the ball.15:33
The ball is sent over by Liam Rosenior, clearance made by Paul Robinson.15:10
Unfair challenge on Stephen Quinn by Christopher Burke results in a free kick. Direct free kick taken by Stephen Quinn.13:31
Assist on the goal came from Jay Simpson.13:31 Goal scored
Goal! - Sone Aluko - Birmingham 0 - 1 Hull Sone Aluko finds the net with a goal from close in to the bottom left corner of the goal. Birmingham 0-1 Hull.12:41
Wade Elliott takes a shot. Blocked by Abdoulaye Faye. Corner taken by Christopher Burke from the right by-line, save made by Ben Amos.12:22
The ball is swung over by Nikola Zigic.8:52
Hayden Mullins gives away a free kick for an unfair challenge on Robert Koren. Strike on goal comes in from Sone Aluko from the free kick.7:36
The ball is delivered by Jonathan Spector, Ahmed Elmohamady fouled by Nikola Zigic, the ref awards a free kick. Ben Amos takes the free kick.6:44
The referee blows for offside against Nikola Zigic. Free kick taken by Ben Amos.5:48
Ahmed Elmohamady crosses the ball, save made by Jack Butland.5:24
Sone Aluko takes a shot. Save by Jack Butland.3:30
The ball is delivered by Christopher Burke, clearance by Stephen Quinn.0:00
The match begins.
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