Round one done and it's a very strong start by Lutalo Muhammad. He got in a three-point shot and has the advantage at the moment.

Take a bow Asha Philip, Desiree Henry, Dina Asher-Smith and Daryll Neita. Great Britain's first medal in this event since the LA Games in 1984!

Britain take bronze in 41.77.

You can't beat a relay for sprint drama. AWAY!

Lutalo Muhammad knocks Cheick Sallah Cisse to the ground straight from the off. Good start.

US. Or Jamaica. Or Great Britain?

Trinidad & Tobago? Loads of pace on display here. 

A bow and we are off. 

Lutalo Muhammad is up against Ivory Coast's Cheick Sallah Cisse remember.

Confirmation that Great Britain have appealed against their disqualification in the 4x4 relay. More on that in a minute, after this other relay...

Nick Hope
BBC Sport in Rio

Lutalo is a very confident character. he's proud to represent Great Britain, and he wants to put on a performance to get the crowd on his side.

He's come through some tough fights already but this is on another level but he'll love fighting in this atmosphere.

Right then. Here we go. Lutalo Muhammad is entering the arena, waving his fist in the air. The British contingent of the crowd respond by waving Union Jacks and cheering loudly. Plenty of support for the Brit. He looks confident.

Will it be yet another medal for US sprinter Allyson Felix? The US woman took silver in the 400m. Now she's on the 100m.

The American first leg comes from long jump champ Tianna Bartoletta too. They are in lane one after their baton drop drama. 

Ekaterini Stefanidi is the first woman to clear 4.85m. Into gold position. 

Michael Johnson
Four-time Olympic gold medallist athlete on BBC One

There will be an appeal. I haven't been involved in so much speculation as I have in the next 20 minutes. We need to wait to find out what happened.

Just a few minutes until the women's 4x100m final then.

Here is the GB team:

Asha Philip, Desiree Henry, Dina Asher-Smith, Daryll Neita.

Can they grab a medal?

The studio panel have just seen 20 replays of Martyn Rooney's changeovers - they still don't know really why Great Britain have been kicked out.

Lutalo Muhammad is going for Great Britain's 25th gold of the Games. No pressure.

He is up in around five or 10 minutes, but here's a reminder of how he won his semi-final fight while you wait.

It was a truly odd scene!

Defending champions United States reached the women's Olympic 4x100m relay final at the second attempt after dropping the baton in their heat.

The Americans ran on their own in the Olympic Stadium after successfully arguing they were obstructed in the first race earlier on Thursday.

They ran 41.77 seconds to beat the time set by eighth-fastest China.

Britain were second (41.93) in their heat behind Jamaica (41.79).

Kenya's Vivian Cheruiyot wins gold in the women's 5000m final whilst also breaking the Olympic record in a time of 14:26.17.

Holly Bradshaw and her coach have disappointment etched on their faces. So much pain. So much effort.

She jumped a season's best though.