Usain Bolt and the controversial Justin Gatlin will get the world championships off to an explosive start when they take their rivalry onto the Beijing track in the 100m heats on Saturday.
Bolt has dominated sprinting since he claimed a golden treble at the Beijing Olympics in the Bird`s Nest stadium, winning nine of 10 individual world and Olympic sprint titles since 2008 -- his sole blip being the 100m at the Daegu worlds in 2011.
America`s Gatlin is the man in form but he cuts a contentious figure after serving two doping bans, latterly between 2006-2010 after a positive test for testosterone.
That suspension came after he had won Olympic 100m gold in 2004 and a world sprint double in Helsinki in 2005.
Since his return, he has won 2012 world 60m indoor gold, London Olympic 100m bronze and Moscow world silver, and at 33 is riding an unbeaten streak of 27 races dating back to August 2013.
Bolt leads the head-to-head against Gatlin 6-1, but the Jamaican insisted statistics, and the fact Gatlin was allowed to compete, were far from his thoughts.
"Competition is competition. It`s always about who`s in the best form and executes," he said. "Rules are the rules, he`s served his ban and he can compete.
"I`m not worried. I never look at statistics. It`s track and field -- you never know what`s going to happen."
Bolt, who has held the 100m and 200m world records since 2009, said he had got over pelvic joint pain that had prevented him from employing enough flex to fully drive the power out of his long legs.
Last month he roared back from that early-season setback, which saw him miss six weeks of competitive action, with back-to-back 100m times of 9.87sec at the London Diamond League meeting."I would have liked more competitive races," Bolt acknowledged. "But training is more important than competing."
On 100m times recorded in 2015, Bolt is now ranked number six. Gatlin tops the list with a personal best of 9.74sec set in Doha in May, having also clocked 9.75 twice and 9.78.
"My body feels it`s like a 27-year-old instead of a 33-year-old who`s run those four years and feels tired," Gatlin told AFP in an interview last month.
"My being away from the sport has been a gift and a curse in a way. For me it`s saddening I had to be away, but I`m able to have had adequate rest and sit back and see my opponents and their growth and use that to my advantage."
Gatlin "is running very well, as far as I can see", said Bolt`s team-mate Asafa Powell, who has clocked up more sub-10sec 100m runs than any other sprinter.
The former world record-holder, however, has misfired on the biggest stage, but has looked in fine form this season.
"Definitely I`m ready to compete, that`s why I`m here," said Powell, who is also captain of the Jamaican team.
"If my best is not as good as other guys, I just have to be happy I gave my best."
Another veteran likely to be in the mix is American Tyson Gay, who has served a one-year doping ban and like Gatlin and Powell is also 33, while 20-year-old Canadian Andre De Grasse will also be sure to draw some attention.
De Grasse, a late convert from basketball, ran wind-assisted times of 9.75 and 19.58 in winning the NCAA 100m and 200m titles this year and followed up with a 10.05 and 19.88 double at the Pan American Games, all of which suggests his legal best of 9.95 may be under-estimating his potential.