Olympic champion and world record holder Usain Bolt has blasted out a World Championship warning with a victory in the 100-metres race at the London Diamond League meeting. The Jamaican sprinter won in 9.87 seconds, the same time he had set in winning his heat earlier at the London Olympic Stadium.This was Bolt's first appearance in six weeks with his only previous 100 metres race this year seeing him struggle at 10.12 seconds in Brazil.American Justin Gatlin still leads the way with 9.74 seconds in the 100 metres this season, setting up an intriguing World Championship showdown with Bolt in Beijing next month.