Berlin  - Two-time reigning champion Allyson Felix leads the way as the United States starts its sprint comeback effort against Jamaica on Friday in the women's 200 metres at the world championships.

Jamaica was expected to take a 3-0 lead into the race unless Usain Bolt was to befall some unforeseeable disaster in the men's 200m later Thursday.

Bolt won the 100m in stunning world record of 9.58 seconds on Sunday and Shelly-Ann Fraser the women's dash the next day.

The Jamaicans blanked the Americans 5-0 at the Olympics in Beijing last year, the Americans only escaping a complete 6-0 humiliation because the Jamaican women threw away the baton in the 4x100m relay final.

The US team will want to avoid a similar embarrassment in Berlin and the omens are not bad. Felix is the fastest woman of the year with 21.88 seconds and Jamaican Olympic champion Veronica Campbell-Brown does not look quite as sharp last as last year.

"I am determined and focused. I feel fresh and I am having fun," said Felix. "I never run for the time in the final but I think it is going to be really fast."

More gold for the US is almost a foregone conclusion in the men's 400m where Jeremy Wariner aims to avenge his Olympic defeat to compatriot LaShawn Merritt with a third straight gold.

Both have looked good but Merritt may have a slight psychological edge because he beat Wariner for the first time last year in the Olympic Stadium at the Golden League meet.

Merritt ran a 2009 world leading 44.37 in the semis, with Wariner, who has returned to his old coach Clyde Hart after the Olympic meltdown, clocking 44.69 seconds in his race.

"Jeremy Wariner? He is in the final and the main competitor ... I am confident coming out of the Olympic title last year, confident from my training, confident from the fans here," said Merritt.

Wariner said that he is seeking redemption: "I want to ... show everybody that I'm not over. I'm not done. I've still got a long career."

If things go really well on the night the US could take another gold, in the women's discus from Olympic champion Stephanie Brown Trafton after three-time champ Franka Dietzsch crashed out in qualifying.

"I feel like I have something to prove. I love being the underdog," said Brown Trafton after barely making the final.

The event seems wide open and so does the men's high jump where holder Donald Thomas of the Bahamas failed to qualify and Russian Olympic champion Andrey Silnov is sidelined with injury.

Having cleared 2.35m this year, Russians Yaroslav Rybakov and Ivan Ukhov are light favourites, with Rybakov seeking gold at last after worlds silvers 2005 and 2007 and Olympic bronze last year.

The day's action starts with the gruelling 50km walk in downtown Berlin. European champion Yohann Diniz of France, Olympic champ Alex Schwazer and Russian Denis Nizhegorodov are top contenders in the injury-related absence of Australian holder Nathan Deakes.  (dpa)