Justin Gatlin's introduction to the crowd goes down like lead. Jeers all around.

They are down on their blocks...

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We are hitting the Hunger Games end of the 100m competition. This is the nasty, brutish and short part of the quickest race on the card.

Only the first two from each of the three semi-finals will get into the final, with a paltry two fastest loser spots to rely on.

This first semi-final features American former world and Olympic champion Justin Gatlin, Jamaica's Julian Forte - the fastest man in the opening heats at 9.99 seconds and South Africa's Akani Simbine - who has gone sub-10 eight times this season, but looked off that sort of pace in the heats.

Flying the British flag is James Dasaolu. He has not been sub 10 seconds since 2013. Now would be a good time to taste single figures again.

Tom Fordyce
Chief sports writer at London Stadium

So three 100m semi-finals. Gatlin in the first with Dasaolu; Blake and Prescod in the second, Bolt, Coleman, Ujah and Vicault in a stacked third. First two men past the line in each semi straight into final, plus next two fastest qualifiers.

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

Image source, Getty Images

We will learn a lot in these semi-finals. Yesterday left a lot, with Bolt questioning the blocks. In these semi-finals we will see things take shape a little more but I think we are going to see a race tonight.

He is more vulnerable than in the past. But that is why he will probably win because he understands that pressure and he understands how it impacts on his rivals. He feels pressure but he knows how to manage it better than anyone else. Others don't know how to do that.

That is why he will probably win when he's not at his best. If the others can produce two more performances, maybe they can win.

Usain Bolt is on his way to the call room. During the recent I Am Bolt documentary, he spoke regularly about his nerves.

He doesn't half hide them well.

Denise Lewis
Olympic heptathlon gold medallist on BBC TV

KJT lost around 200 points in the high jump. It's massive. You really are compromised without a good high jump in heptathlon. She has to dig deep now. She knows she can throw 13m but it's whether she has left the baggage behind. She has got to be aggressive, I want to see her be aggressive.

Jessica Ennis-Hill
London 2012 Olympic heptathlon champion on BBC TV

It's going to be a tough event for KJT. She's capable of clearing 13m which will gain her a few points but Thiam is a fantastic thrower, capable of 15m.

We are after your one-word summary of Usain Bolt tonight.

Make them as functional or surreal as you fancy and hit us up on #bbcathletics., external

And there will be some of athletics' good and great having a shot on the BBC Sport social media channels as well.

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The reallocation of major medals continues apace in the aftermath of the Russian doping scandal.

Britain's Jo Pavey poses with her bronze medal during the medal reallocation victory ceremony for the women"s 10,000m athletics event from the 2007 World Championships in Osaka.

So, now Dame Jessica Ennis-Hill has retired (and has come to help commentate on the athletics with the BBC), we asked her how she thinks she would get on in an alternative heptathlon....

If you want to find out how to get into (normal) athletics, take a look at the Get Inspired guide.

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Next up for Katarina Johnson-Thompson is one of her weakest events - the shot put.

Her best is more than two metres down on leader Nafi Thiam's. After badly denting her medal hopes in the morning, Johnson-Thompson could do with pulling something special out of the fire now.

The Briton is down in fifth overall.

Any half-half Bolt-Ujah versions knocking about mate?

App users may need to click the link to see Michael Johnson's tweet.

All was not right in the court of Usain Bolt yesterday.

Athletics' jester-in-chief had to dig himself out of a sluggish start to win his heat over the last 40m in a time of 10.08.

He shook his head as he cross the line, he had a moan about the blocks in his post-race interview and, possibly in the privacy of his hotel room, pondered on rival Christian Coleman's slick 10.01 second showing.

Today, it is semi-final time. With British pair CJ Ujah and Reece Prescod also contending for spots in the final at 21:45 BST.

Image source, EPA

Earlier today Martyn Rooney tweeted: "No excuses, just not good enough. Left it on the track and it was too slow. Smash it Dwayne Cowan and Matt Hudson-Smith."

It tells you all you need to know about his 400m heat. The 30-year-old placed sixth when a top-three berth was needed to progress from any of the six heats.

His shout out for Cowan worked as he went very close to a PB on his way to third in his heat - clocking 45.39 for the lap. And Hudson-Smith crept through too as a fastest loser. He was fifth in the first heat but a mark of 45.31 sees him through to the semi-finals.

Wayde van Niekerk is of course the poster boy for this distance and eased through in 45.27, while American LaShawn Merritt - silver medallist at the last worlds - ran 45 flat.

Most importantly though it seems a Rooney shout out brings good things.

Paula Radcliffe
Women's marathon world record holder on BBC TV

Getting ready for a 100m final is so big but when it's your last race and you've made that public, the emotions must be huge. I think they will come out later, maybe when he's crossed the line or is on the podium.

Watch Paula and the team on BBC One now, just click 'BBC Coverage' in this live text.

Katarina Johnson-Thompson's chances of getting a medal in the heptathlon improved this morning as Latvian world bronze medallist Laura Ikauniece-Admidina withdrew from the competition following an injury in the hurdles.

But things went south from there.

Johnson-Thompson cleared 1.80m with her first jump in the high jump competition, duly skipped 1.83m and then disasterously fouled out at 1.86m.

Her mark of 1.80 is 18cm off the British record she set in Rio last summer. The difference between between the two mark in heptathlon terms is a whopping 233 points.

KJT is fifth on 2053 points after the first session, 162 behind leader and Olympic champion Nafi Thiam.

Ouch.

Usain Bolt was born In August 1986 to parents Wellesley and Jennifer. One of them claims they gave him his dance moves. Which one? Find out by clicking play below.

They claim Usain has a lot of love to give. Now that he's about to call it a day, he can spend more time handing out the hugs and cuddles eh?

Four-time Olympic champion Michael Johnson said Usain Bolt's opening 100m of the World Championships "looked a little weird".

As you may have read, Bolt was not happy with what he said was a "very bad" run. So how big a task does he have on his hands this week? Johnson believes a big one, stating the great man has "never been more vulnerable".

Drink in his views by clicking play below.

If the action in the stadium has already got you thinking 'I fancy a bit of that', you can join one of the London 2017 Team Personal Best events taking place across the country during the championships, like these guys did....

Image source, Team Personal Best

You can find your nearest event here.

And if you want to find out how to get into athletics, take a look at the Get Inspired guide.