Justin Gatlin laid down a marker by clocking the fastest time in the 100 metres heats at the World Championships in Beijing on Saturday ahead of his eagerly awaited showdown with Usain Bolt.

The controversial American, twice banned for doping, has been tipped to dethrone Bolt in Sunday's final following a run of 27 consecutive victories and the 33-year-old stated his intent by clocking 9.83 seconds to ease to victory in heat six.

Six-time Olympic gold medalist Bolt had an opportunity to respond in the next heat and was clearly not at full tilt as he edged out Mike Rodgers in a time of 9.96secs at the Bird's Nest. 

Defending champion Bolt, who celebrated his 29th birthday on Friday, will be hoping to rise to the occasion when it matters in the final as he eyes yet another title at the expense of Gatlin.

Asafa Powell was also quicker than his fellow Jamaican as he won the opening heat in 9.95secs, with Tyson Gay (10.11), Femi Ogunode (9.99) Trayvon Bromell (9.91) and Jimmy Vicaut (9.92) winning the other heats.