Two World champions are seeking first-time sprint doubles in Daegu. Only one will have the possibility of success, as they meet in the middle over 200m.
Veronica Campbell-Brown already has a 100m World title to her credit from Osaka in 2007, but although she has won two Olympic titles at 200m, she has had to satisfy herself with silver medals at that distance in the last two World Championships as Allyson Felix defended her title not once, but twice.
And Felix, once again, is a major threat to the Jamaican’s ambitions in what she hopes will be the second leg of a 200/400m double in Daegu.
The 25-year-old from Los Angeles is recognised as a 200m specialist although, in a mirror image of her last two World Championships, she has taken silver behind Campbell-Brown in the last two Olympics.
But while she is confident of winning a fourth successive world title over 200m, she confesses she is “outside her comfort zone” in seeking a double she hopes to repeat at London 2012, particularly as the 400m event comes first.
This year she became the first-ever sprinter to complete a set of US titles in the women's 100, 200 and 400m to underline her strength across the sprint distances.
"I'm looking forward to trying something new out there in Daegu," said Felix this month.
"I'm kind of stepping outside my comfort zone with the 200m and 400m double.
With the 400m first, that was real dilemma in deciding if I wanted to go for it or not.
"For me, it would have been much easier to decide if the 200m was first being that it is my primary event and I think it is easier to sprint first.
"I think the most difficult thing is trying to come off three rounds of 400m and then sprint again.
"But I think it will be a real learning curve and be really interesting.
"Hopefully it will go well but I think most of all, I'll learn a lot for the schedule and participating in it ahead of London 2012.”
But these two champions cannot afford to concentrate their competitive energy solely on each other given the strength of the rest of the field – and particularly in the presence of Felix’s team mates Shalonda Solomon and Carmelita Jeter, respectively first and second in the US trials.
Solomon’s winning time of 22.15 in Eugene heads this year’s world list, with Jeter one place behind her thanks to her winning effort in a personal best of 22.20 at the Samsung Diamond League meeting in Monaco on 22 July.
Campbell-Brown’s best this year is 22.26, which she ran in Budapest on July 30, while Felix’s season’s best is the 22.32 she registered in chasing home Jeter at the Monaco meeting.
In terms of championships, Jeter knows what it feels like to finish ahead of Campbell-Brown, although it was over the 100m, where she took bronze ahead of the Jamaican in the last World Championship final in Berlin, when Campbell-Brown was the defending champion.
Russia’s Anastasiya Kapachinskaya, with a 2011 best of 22.55, is another contender to be reckoned with, as is Campbell-Brown’s team-mate Kerron Stewart, who ran 22.63 in June as she finished runner-up to the double Olympic champion at the national championships in Kingston.
Jeneba Tarmoh, who took the third qualifying place at the US trials, will also fancy her chances of making an impact here, given that the athlete she denied an individual place to was Bianca Knight, who is currently four points clear of Felix, and five points clear of Jeter, at the head of the Diamond Race for this event.
Mike Rowbottom for the IAAF