Bolt dominated the Beijing Games four years ago, winning golds in world-record times in the 100, 200 and 4x100 relay - something no man had ever done at an Olympics. At the 2009 world championships, he lowered his 100 mark to 9.58, which still stands.

But he's been less-than-outstanding more recently. A false start knocked him out of the dash at last year's world championships, and he lost to training partner Yohan Blake in the 100 and 200 at the Jamaican Olympic trials.

His reaction time Saturday was only sixth-best in his eight-man heat Saturday.

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