By Gary Smith, World-Track

BERLIN — American sprint legend Michael Johnson believes Tyson Gay must get a fast start when he clashes with Usain Bolt over the 100 metres or the race will be over within a few metres.

Johnson, the current 400m world record holder who held the previous 200m world mbest, before losing it to Bolt last year, says even a fast finisher like Gay would have a difficult time in fending off the towering Jamaican if he gets out with the field.

"Gay understands that his only chance of beating Bolt is to take the lead early and exploit Bolt’s only weak spot, which is his start," Johnson said.

"Unfortunately for Gay, the start of the 100m is only the first 10 per cent of the race and so that is Gay’s small window of opportunity.

"He then has to hold that lead for the remaining 90 per cent against an athlete who, I have been told, is capable of covering the 100m in 41 steps compared to mid-forties for the average sprinter."

Gay will start the championships as the defending sprint double champion, after over taking Asafa Powell to win the 100m and blasting away from Bolt to take the 200m two-years-ago in Osaka.

But Johnson reminded that things would be more difficult for his fellow American, as Bolt had already grown out of being a potential world beater and has immerged into the world superstar he now is.