Use play icon to watch live coverage alongside commentary from Vicki Sparks & Stephen Warnock
Also listen to commentary from BBC Radio Manchester & BBC WM 95.6
Man City are fifth in the Premier League, Birmingham are 18th in the Championship
Man City are six-time winners - last in 2019
Birmingham were runners-up in 1931 & 1956
Alfie May (74 mins)
That had been coming for quite a while.
Alfie May has threatened all afternoon for Cheltenham, and this time he buries a great finish into the corner from the after cutting inside from the left.
We go straight to extra time and penalties in any tie that finishes level, remember.
Man City 3-0 Birmingham City
Stephen Warnock
Ex-Leeds and Liverpool defender on BBC TV
Bernardo Silva is usually so composed in front of goal but he snatches at this one. It was poor technique and you don't often say that about him.
Man City 3-0 Birmingham City
Bernardo Silva is beginning to look frustrated in his search for a hat-trick goal, as he drags anotehr shot well wide.
Changes for both sides once again.
Fernandinho replaces Rodri for Manchester City, while Jeremie Bela and Lukas Jutkiewicz are on for the visitors.
Chelsea 3-0 Morecambe
Chelsea go close to a wonderful fourth goal but find Morecambe goalkeeper Mark Halstead a big barrier.
Mason Mount cuts open the Shrimps defence to find Cesar Azpilicueta. His cross is touched towards goal by Olivier Giroud but Halstead blocks and the big keeper is up quickly to deny Mason Mount from the rebound.
Great keeping.
Crawley Town 3-0 Leeds United
Martin Keown
Former Arsenal defender on BBC One
This is no more than Crawley deserve.
Image source, Getty ImagesBarnsley 1-0 Tranmere
Morgan Ferrier runs off for Tranmere to be replaced by Corey Blackett-Taylor.
My mate Chris once scored an equaliser against me on Fifa with Blackett-Taylor - he'll be praying for a similar kind of impact if Tranmere are going to rescue this Cup tie.
Jordan Tunnicliffe (70 mins)
Tunnicliffe fires home third for Crawley
Unbelievable!
It's scrappy in the Leeds box, and Ashley Nadesan musters an effort on target.
Kiko Casilla gets down well to keep it out, but Jordan Tunnicliffe is there on the edge of the six-yard box to take a touch and hammer it into the roof of the net.
Surely game over?
Cheltenham 0-1 Mansfield
The equaliser just won't come for Cheltenham Town.
The Robins have had 16 attempts to Mansfield's three - but Mansfield's only shot on target sees them 1-0 ahead with around 25 minutes remaining.
Alfie May's shot from distance is the latest to be saved by Marek Stech.
Chelsea 3-0 Morecambe
It doesn't get any easier for Morecambe as Chelsea make two changes.
Timo Werner and Hakim Ziyech have done their damage so Christian Pulisic and Olivier Giroud come on to replace them.
Bristol City 1-1 Portsmouth
Alfie Mawson, who was returning from a knee injury today, makes way for Taylor Moore. Nahki Wells is also on for Hakeeb Adelakun for Bristol City.
Crawley Town 2-0 Leeds United
Leeds have just over 20 minutes to try to stop themselves exiting at this stage of the competition for the fourth successive season. At the moment though, Crawley are camped in their half and Sam Matthews' awkward strike is tipped wide for a corner.
Barnsley 1-0 Tranmere
Valerien Ismael makes some changes for Barnsley. The lively Conor Chaplin is off to be replaced by Vicyor Adeboyejo. Michael Sollbauer is also off as Toby Sibbick takes to the field.
Man City 3-0 Birmingham City
Stephen Warnock
Ex-Leeds and Liverpool defender on BBC TV
Riyad Mahrez just goes a bit too early but it just shows the small margins that you are coming up against when you play against Manchester City.
Man City 3-0 Birmingham City
Riyad Mahrez thinks he's scored Manchester City's fourth as he nips in at the back post from a cross, but the flag immediately goes up for offside.
It goes to a VAR check, but the decision is upheld and it remains 3-0.
#bbcfacup or text 81111 (UK only)
Lynne: It just shows you how small teams that have nothing to lose in the FA Cup can play their hearts out and show bigger teams up!!
Will: The biggest shock is, this isn’t a shock at all. We don’t have a squad capable of dealing with any form of rotation. Poor, poor performance.
Conrad: Sorry but I'm starting to think there's a touch of "the Emperor's New Clothes" about Bielsa and his tactics.
Chelsea 3-0 Morecambe
Triple substitution for the visitors.
John O'Sullivan, Liam Gibson and Kelvin Mellor on in place of Stephen Hendrie, Jordan Slew and Ryan Cooney.
Chelsea 3-0 Morecambe
Bristol City 1-1 Portsmouth
Half a chance for Antoine Semenyo as he reacts quickest to flick a left-footed effort on goal, but Craig MacGillivray is down well to gather.
Man City 3-0 Birmingham City
Stephen Warnock
Ex-Leeds and Liverpool defender on BBC TV
It's lovely interchange from Manchester City but Andrés Prieto is very lucky there - he just comes out and misjudges it.
Bernardo Silva is then unlucky from the corner, he just can't quite get it out of his feet. It would have been an ugly goal for his hat-trick.
Image source, ReutersMichal Helik (59 mins)
Barnsley have the lead and it's a really nice header from Michal Helik .
Herbie Kane's initial corner is cleared but when the Barnsley man gets it back, he floats in a delicious cross and the big defender powers it home.