Muhammad has a look behind to see where McLaughlin is and it slows her down a touch.

But she's still clear. Just.

Coming round the final bend, Muhammad is still just ahead of her compatriot but these two are clear of the rest of the field.

Muhammad is making fast progress, she's up on McLaughlin.

McLaughlin or Muhammad?

On your marks...

Michael Johnson
Four-time Olympic gold medallist athlete on BBC TV in Doha

This is going to be a very interesting race. It's really a head to head - Syd McLaughlin v Dalilah Muhammad and then everybody else.

I think McLaughlin has a bit of a chip on her shoulder. She's seen Muhammad break the world record at the US Championsihps and now she wants to do something special.

McLaughlin has lost to Muhammad twice this year but she's on the inside lane of Muhammad tonight and I think the edge goes to her. She's really hungry.

Right, time for the first final of the night - the women's 400m hurdles final.

Can Diamond League champion Syd ‘The Kid’ McLaughlin (lane four) come of age and win a maiden global title? Or will American rival and reigning Olympic champion Dalilah Muhammad (lane six) end her world record-setting season with her first world title?

I think you'd be pretty safe to put your money on an American...

So here's how the men's 4x100m relay final will look.

GB sitting pretty at the top. The USA in there by the skin of their teeth.

KJT finally has the bling around her neck.

She won't be letting that medal out of her sights for a long time. If ever!

Michael Johnson
Four-time Olympic gold medallist athlete on BBC TV in Doha

Great Britain were very smooth and very quick. They were showing their speed.

The Coleman-Gatlin hand-off wasn't very good but Gemili's was very good.

Watch it for yourself.

Michael knew...

Andrew Cotter
BBC Sport commentator in Doha

The result from the first semi-final has gone green - the United States are still in.

The USA seem to have avoided disqualification after their race - and their handovers -remained under review for a loooong time.

Mutaz Essa Barshim goes sailing over 2.30m to put himself up into second place.

That's the first time he's cleared that height since his 14-month injury lay-off and he's got a clean sheet so far.

Colin Jackson
Two-time world 110m hurdles champion on BBC TV in Doha

Canada should have been better. They lost all their ground on the first leg and first exchange. It was so pedestrian compared to all the others.

That was an incredibly fast race - six times under 36 seconds is truly sensational.

It's South Africa who take it in 37.65

Japan second, China third.

Canada - with Andre De Grasse on the anchor leg - finish way down in sixth.

China seems to lose it on the third leg, however, as Canada, France and the Netherlands get themselves into it alongside South Africa.

China and South Africa with the best starts.

Safely away in heat two.