Andy Lake:  My heart goes out to KJT she would have won gold, Denise Lewis had her red flag changed to white in the exact same situation, #bbcathletics, external

Jon Hobson:  Its nearly Jess time! #bbcathletics, external#Beijing2015, external

Claire Turner:  Oh my world #KJT, external My heart is literally breaking for you. Own that 800m.

Kelly Sotherton
Former British heptathlete on BBC Radio 5 live

"This has been a traumatic experience for Katarina. She's been distraught all day, with tears in her eyes, but she will learn from this and come back stronger."

Image source, Reuters

Daley Thompson
Two-time Olympic decathlon champion on BBC TV

"KJT won't want to be out there at all, because she'll be a bit embarrassed about what has gone on today. But she needs to compete to make sure she can go in the long jump later this week."

Katarina Johnson-Thompson still being made to wait until she can bring an end to a horror of a day. She waves to the camera, but it isn't the ebullient KJT we usually see. 

The Briton and American Barbara Nwaba by the far the quickest athletes on paper. Johnson-Thompson off slowly, content to jog around for two laps, perhaps keeping the long jump in mind. 

Ben Wire: @J_Ennis, external = inspiration; KJT lucky to train/compete with a legend. So excited about 100m, glued to live-feed here in France.

Harry J:  Athletics World Champs. Rest of day sorted.

Paul Hetherington: @J_Ennis, external#simplythebest, external#bbcathletics, external Good luck in the 800. Amazing #rolemodel, external

All on board! There's no separating Jimmy Vicaut, Trayvon Bromell or Bingrian Su after the trio clocked 9.99 seconds in their semi-finals so they're all on the 100m final bus.

John Ryan:  No matter how quick he is, why is two-time drugs cheat Justin Gatlin racing at all!! Bums on seats obviously what matters most.

Matt James:  Bolt won't have a problem, he can handle Gatlin any day of the week.

Stuart Wickham:  Would love to be proved wrong, but Usain's got as much chance of winning as my Aunty Doreen.

The 800m for the heptathlon is about to start. A downcast Katarina Johnson-Thompson is on the track, no words, no quick time over these two laps, will soften the disappointment. 

Image source, BBC Sport

Tom Fordyce
Chief sports writer

"Justin Gatlin's camp very confident ahead of tonight's 100m showdown. Two stand-out things from my chat with the inner circle: (1) They want their man in the lane next to Bolt in the final, because they believe a fast Gatlin start will intimidate and then derail the big man, and (2) Their man is ready, on this very fast Bird's Nest track and for the first time in his career, to run under 9.7 seconds."

Michael Johnson
BBC Sport athletics expert & 400m world record holder

"Usain Bolt is the best there's ever been and anything is possible, but he is in big trouble right now. I'm not crazy about his technique at the start where he drags his foot. I'm not sure you get that much out of it.

"He's starting to question 'should I have come out here?' He's got one more round to go and he will be aware of what Justin Gatlin did in his semi-final." 

Image source, Getty Images

So, having chatted quite a bit about the 100m, it seems only right to ask for your 100m final predictions. Who will finish in the top three and perhaps the bold among you can guess the times, too. Tweet us using the hashtag #bbcathletics or text 81111

Here's the prediction of our chief sports writer Tom Fordyce: (1) Gatlin 9.68 (2) Bolt 9.79 (3) Gay 9.88.

Justin Gatlin's 100m semi-final time of 9.77 seconds was impressive - and in fact it would have won four of the last five World Championships. Here's the pedigree:

2013 final - 9.77secs - Usain Bolt

2011 final - 9.92secs - Yohan Blake

2009 final - 9.58secs - Usain Bolt

2007 final - 9.85 secs - Tyson Gay

2005 final - 9.88 secs - Justin Gatlin

Image source, Getty Images

After going out in the semis of the 100m, Britain's Richard Kilty told the BBC: "It was amazing to be out there, but I'm really disappointed with that. I'm still a little rusty and this is definitely something to build on. 

"I'm without a coach and coaching myself at the minute and this race probably came a little too soon for me, but now it's on to the relay and hopefully we can compete for medals there."

Kilty finished eighth in 10.20 seconds. 

Image source, PA

Darren Campbell
Former British sprinter on BBC Radio 5 live

"Gatlin is 2-0 on Bolt up after yesterday and today's semi-finals but the final is all about who can hold their nerves. Anything can happen, the tension is so different, and that's what we have to hold on to.

"It's not over. I don't know who will come third - I'm not even sure who will come second!"

Colin Jackson
Two-time world 110m hurdles champion

"That race was a proper battle. Tyson Gay's training hasn't gone perfectly but he's a competitor. Jimmy Vicaut could have run better and I'm a little disappointed with him."

Image source, AP

Michael Johnson
BBC Sport athletics expert & 400m world record holder

The third semi-final. A great start from Britain's Richard Kilty, but as you expect, he fades away. Tyson Gay comes through, pipping Asafa Powell in second (9.97). Frenchman Jimmy Vicaut was third in 9.99. 

If the next lot can better Justin Gatlin's semi-final time then pigs will start climbing trees. But it's still worth a watch, just to see who finishes in the top two because, on paper, this is a tough one between Gay, Powell and Vicaut.  

Lane 2: Hassan Taftian (Iran)

Lane 3: Richard Kilty (GB)

Lane 4: Jimmy Vicaut (Fra)

Lane 5: Tyson Gay (USA)

Lane 6: Asafa Powell (Jam)

Lane 7: Ramon Gittens (Bar)

Lane 8: Churandy Martina (Ned)

Lane 9: Ben Youssef Meite (CIV) 

Image source, PA

Darren Campbell
Former British sprinter on BBC Radio 5 live

"This has been billed as good versus evil. Even Usain Bolt won't want that huge responsibility. One athlete has to save the sport all on his own. The people to blame for the situation are not Gatlin or Bolt but the people running the sport"