Daegu (South Korea): Jamaican sprint ace Usain Bolt has assured fans that he usually saved his best for big events, as the 13th World Championships prepared to open here on Saturday.

By his lofty standards, the World and Olympic champion has not been at is best over the last two seasons and has especially looked below par this year though he is undefeated.

However, the 25-year-old will turn his attention over the next week to defending his 100 and 200 metres titles and believes he is on track to dominate again.

'At the championships, I believe I am much more focused. Even when I have not been doing well in training, and I have been messing up, when it comes to a championship I have a real focus because I want it really bad,' Bolt said.

'And now I want it even more because I want to be a legend. I have been working this week. I am focused and I am ready so I am going to get it done.'

Bolt stormed to international prominence at the 2008 Beijing Olympics by capturing the sprint double before returning a year later to dominate the World Championships with mind-boggling times as he repeated the feat.

He clocked 9.58 seconds in the 100 metres and 19.19 seconds in the 200 metres but has been below his record best this year with a season-best 9.88 seconds and 19.86 seconds respectively.

Bolt said, however, he regarded this season as a 'comeback' one as he rebounded from the injury that cut short his campaign last year.

'I am coming back from injury and I am working really hard to get back into tip-top shape. I don't think I am in 9.5 shape, but I definitely will be able to run fast,' he explained.

'I wouldn't say it was more difficult to win than in 2009, although there is a lot of guys running fast, and I am not in tip-top shape which I was in Berlin. But I think I am focused and I am ready now.' Bolt also dismissed suggestions that he would be under a heavy weight of public expectation to repeat his scintillating performances of the past.

'I think people expect a lot from me. Personally I am focused on winning. To me, pressure is always there. It was there even before I won my first gold medal,' he stressed.

'But I don't look at it as pressure. I just look at it as 'everyone wants the best from me', so I just go ahead and do my race.' Bolt's 100 metres title defence was made even easier Thursday when his major threat Asafa Powell pulled out with injury.

American Tyson Gay, who was expected to challenge Bolt in both sprints, was also forced out of the showpiece after pulling up injured at the United States National Championships in June.