Marc Albrighton floats a ball over to Demarai Gray on the right. A couple of stepovers help him beat the full-back and he lifts it into the six-yard area.

It's just slightly too high for Ayoze Perez, who can only head it upwards before it's cleared.

Danny Ward punches away the first corner of the game.

Brentford have had a few half-chances. This is their best effort so far.

It's just settled down a little bit now. Marc Albrighton has a heavy touch but Wes Morgan is on hand to poke it clear.

Morgan then blocks Jan Zamburek's cross on the left and Brentford have a corner.

Pat Nevin
Former Chelsea and Scotland winger on BBC Radio 5 Live

I'm sure you have noticed - we're playing FA Cup rules today. Some things that would normally be yellow cards aren't even being coinsidered... It's making for a better game! In the FA Cup you get more leeway, under these rules they're basically allowed to assault you!

Better from Brentford, who is starting to squeeze out the gaps Leciester were finding so easily early-on.

Another attack breaks down but Leicester have a throw-in on the left.

Jermaine Jenas
Ex-Tottenham and Newcastle midfielder on BBC Match of the Day Live

Brentford are starting to find a few gaps now. Sometimes it can take you a while when you come up against such a good team. Dervisoglu was only a couple of yards there from finding the far corner. That was much better.

Nice turn from Dru Yearwood in the middle but a sloppy pass gifts the ball to Leicester. They break down the left through Ayoze Perez before the hosts win it back.

Jan Zamburek then fouls Hamza Choudhury near the touchline.

Decent break from Brentford as Emiliano Marcondes takes control down the right but Leicester's players get back so quickly.

Brentford's players react to the pressure to win the ball back immediately before Jan Zamburek cuts inside and shoots straight at Danny Ward.

Moments later, Halil Dervisoglu does the same and curls one just wide of the right post. Decent from Brentford!

Jermaine Jenas
Ex-Tottenham and Newcastle midfielder on BBC Match of the Day Live

Emiliano Marcondes just couldn't quite get his foot around it but it was a decent enough strike. Half the ground thought he had found the back of the net but unfortunately it's hit the side netting.

Demarai Gray is the one to take it and his effort deflects off the top of the wall and out for a corner.

"Come on Brentford!" scream the home fans.

Free-kick for Leicester in a good position...

Demarai Gray and Christian Fuchs over it.

It will be a very odd occasion for Blues fans today. Ever sat in the away end of your own ground?

Birmingham City boss Pep Clotet: "We've got to prepare like it's an away game, get changed in the away dressing room and travel there on the coach.

"But we know as soon as the players step out onto the grass it's our place. We're kind of brothers sharing a home, which makes it nice."

Image source, Getty Images

Coventry City boss Mark Robins: "There are probably a number of supporters who have stayed away for a number of reasons but clearly, we've got the potential to be a huge club and that's the ambition."

Pat Nevin
Former Chelsea and Scotland winger on BBC Radio 5 Live

Brentford are playing much, much better in the last five or six minutes. That blue wave that came at them was extraordinary, but they've been in the game and trading blows in that midfield area.

It's brilliant play from Mads Rasmussen on the right, as he beats the full-back and whips a decent ball into the box.

Jan Zamburek brings it under control before slipping it left to Emiliano Marcondes, who fires it just wide of the right post and into the side-netting.

Iheanacho's opener for Leicester (3 mins 7 secs) is the third earliest goal scored by a Premier League side in the FA Cup this season after Idah for Norwich against Preston (1:20) and Lo Celso for Spurs against Middlesbrough (1:55).

Can Kelechi Iheanacho get another one?

Jermaine Jenas
Ex-Tottenham and Newcastle midfielder on BBC Match of the Day Live

The work-rate Leicester are putting in is buying them the time to knock the ball around. Very rarely have we seen Brentford making headway into the Leicester half.

Kelechi Iheanacho gets away with a run in behind. It's a tight angle but he forces a save from Luke Daniels from close range.

Sheffield United

Sheffield United are eighth in the Premier League table but manager Chris Wilder is keen to progress in the FA Cup.

"There will always be prioritisation but this is still a competition we have huge history in and would like to go well in."

Looks like Jack Robinson might get a game...

It's all going to script so far. The Premier League side are cruising along.

Image source, Opta

Image source, Opta