Will Bolt or Gay reign supreme in Berlin this summer?
Over the last few weeks Usain Bolt and Tyson Gay have been ripping up race tracks across the globe preparing for the World Championships.
Bolt, triple Olympic champion, is flying and easily won the 100m at London's Grand Prix, while Gay, another Crystal Palace winner, has bagged the fastest 100m (9.77 seconds) and 200m (19.58) this year.
The pair are yet to meet this season and will go head-to-head in Berlin in both sprints. Could there be a surprise in store?
By Steve Cram
Former Olympic athlete and BBC Sport pundit
Bolt has said he's only 75% fit! If that's true he'll be running 9.3 at the Worlds, which won't be happening.
What he's saying is he'll be better in Berlin and you would expect that from the champion athletes at majors. Bolt did it last year in Beijing and Gay did it at Osaka in 2007.
Bolt has clocked some super-fast times recently in the wet and wind of Lausanne and Paris. If he can do that in those conditions he's got to be thinking 'watch out' if he runs on a warm day with a breeze behind him.
Highlights - Bolt blasts 100m field away (UK users only)
Gay will know this though and the mind games will continue. They are two very different characters.
Bolt is the showman, outward going, while Gay is quieter. I thought we might have had a three-way race going into Germany but I think it will be between the two of them.
Bolt's 9.91 run on Friday was good given the conditions but he wasn't as smart out of the blocks as he would like for Berlin. It might be something he could work on.
It doesn't look like he's bothered. He's got so much in hand and it's a shame the 100m wasn't on Saturday because I think we would have seen something pretty special.
Gay has been running well - 20 seconds is good at any stage. He prepares for races well and he can do well if he stays fit and healthy.
It will be interesting to see if he wants to attack both events - he says he is - so we can look forward to two great sprints.
Asafa Powell's the one who keeps writing himself out of the equation. He should be good, should be better and should be quicker but every time he comes up against Bolt he just seems to wilt away.
Bolt should win the Worlds though. The weather could play its part. It won't be like Beijing and if it's warm then we could be looking at a 9.7. A new record may just depend on Bolt and what he fancies.
Gay needs to go out there and put some doubt into Bolt's mind. The Jamaican hasn't been under much pressure before. If Bolt doesn't perform in the first 20-30 metres then how does he respond?
If I was Gay I would put all my eggs in that basket and get out quick and put him under pressure.
Regarding the Brits, there is Simeon Williamson. He is an improving athlete but there are a lot of people currently between him and a medal.
Two things need to happen. He's got to get stronger and quicker or one or two others would have to not perform.
If you look at pure form the medals will be Bolt, Gay and Powell but the target for Simeon should be get to the final and see what happens.
By Darren Campbell
Former GB sprinter and Radio 5 Live pundit
It is always difficult for Bolt to look anything but impressive. It was a strong and very professional display at Crystal Palace but he was also very appreciative of the crowd.
It reminded me of the good old days of Linford Christie, Carl Lewis and Maurice Greene. Nobody has grabbed the sport like Bolt is currently doing for a very long time.
The London Grand Prix is all about the fans and Bolt was not under any pressure. He's Olympic champion and has been touring the world putting on a show.
Highlights - Gay dominates the 200m
Come Berlin there will be a medal and his reputation on the line, so he'll feel an extra 10% of pressure. All he's done before will count for nothing. The nerves will be different but he's an amazing and spectacular championship performer.
On Friday, Bolt did all the work in the first 60m and then came off the gas. He's got a lot more in the tank though and executing his start properly will only add to his confidence.
He also knows if he has a bad start he can catch anybody up. The only person capable of putting doubts in his mind is Tyson Gay. His 200m race in London was a good one, although the field was not great.
I felt going into Beijing that Gay could win but he was unfortunate with his injury. All we want is Gay and Bolt getting it on in the 100m, 200m and relay.
Everybody prepares for races differently but there are no mind games between Gay and Bolt.
Tyson doesn't say much - he just delivers. Usain doesn't bad-mouth his rivals - he also just delivers.
They don't use aggression on the start line or use verbals like some have in the past. I like how these guys are dealing with it all.
Highlights - Gay dominates the 200m
They are really changing how people think and watch the sport and could help to get athletics back to being one of the country's top sports again.
I predict Bolt wins the 100m in the low 9.7s ahead of Gay. I'm sitting on the fence for bronze because I don't think it will be one of the usual suspects.
The 200m will be closer. Gay may not actually run the 100m and if he only runs the 200m then I think he will beat Bolt.
Williamson is an athlete I have been impressed with - especially at the recent trials. He had the right mindset and I think he can go under 10s but I'm going to tell him he needs to run his own race.
In Friday's final he ended up running Bolt's race. He has great strength though and all bodes well - he will make the 100m final.
Cram and Campbell spoke to BBC Sport's Mark Ashenden.
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