Youth and experience combined as Nathan Redmond set up Wade Elliot to open the scoring for Birmingham, but Leeds hit back through Ross McCormack and a penalty from El-Hadji Diouf to go through.
Bournemouth 0-1 Wigan Athletic (Fourth round: Macclesfield Town vs. Wigan Athletic)
A superb goal from Mauro Boselli was enough to give the Latics a win at Bournemouth. A Wigan counter-attack was finished beautifully by the Argentinian, who smashed it into the top corner.
Brentford 2-1 Southend (Fourth round: Brentford v Chelsea)
A chance to host Chelsea provided a big incentive for both clubs in this tie, and it produced a great game. Paul Hayes gave the Bees the lead, before both sides hit the woodwork. Brentford were all over the visitors, but Paul Smith had the game of his life in goal, and saved a penalty from Harry Forrester in the second half. Barry Orr managed to equalise for Southend, but Clayton Donaldson bundled in the winner for the hosts.
Leyton Orient 1-2 Hull AET (Fourth round: Hull vs. Barnsley)
Nick Proschwitz opened the scoring with an incredible 25-yard volley, but Dean Cox's cross floated in late on to take it to extra time. Tom Cairney gave the Tigers the win in the dying minutes.
MK Dons 2-0 Sheffield Wednesday (Fourth round: Queens Park Rangers vs. MK Dons)
The Owls' woes continued as they suffered at the hands of their lesser opponents, goals from Shaun Williams and Dean Bowditch earning them a tie against Premier League QPR.
Stoke 4-1 Crystal Palace AET (Fourth round: Stoke vs. Manchester City)
Alex Ferguson was a notable spectator, with rumours of a Wilfried Zaha transfer abound, but the England forward was taken off at half-time with injury. Kenwyne Jones put the home side in front in the second half, before Ryan Shawcross gave away a late penalty which Glenn Murray smashed home. Palace couldn't hang on throughout extra time though - a Jon Walters double and a Cameron Jerome goal did for them.
After a nervy game, Blackpool looked to have won it as Nathan Delfouneso opened the scoring late on, but Kieran Richardson smashed home a beauty from 25 yards with the last kick of normal time. Blackpool went close to victory on several occasions in extra time, with Kirk Broadfoot and Tom Ince both missing golden chances, and Brede Hangeland broke their hearts with a late goal to win it for the Cottagers.
West Bromwich Albion 0-1 Queens Park Rangers (Fourth round: Queens Park Rangers vs. MK Dons)
England's Jay Bothroyd (yes, it happened) was the hero for the Rs as he steered home a header from a corner to secure a victory in a rather dull encounter at the Hawthorns.