Imperious Usain Boll eased * through the first round of the

Olympic 200m on Tuesday as iT the Jamalcan t0°k the next step towards a sprint double after having already retained his 100m title in style.

Reigning champion Bolt showed no signs of fatigue as he ran the bend hard before relaxing in the home straight and strode over the line to win in 20.39 seconds in the first heat on a chilly morning at the Olympic Stadium.

"This was an easy run. I am enjoying it," said Bolt. "This is my favourite event so I am looking forward to it."

I lis main challenger for the 200m, Yohan Blake, also negotiated his passage into the next round wilh ease, as the Jamaican who took the silver behind Boll in the short sprint won his heat in 20.38 seconds.

Blake said it was possible Bolt's three-year-old world record of 19.19sec could be under threat in the later rounds.

"The track is fast and Usain is fast so anything is possible," Blake said.

European challenger Christophe Lemaitre of France also went through after winning his heat in 20.34 seconds.

The challenge for the United Slates will come from Wallace Spearmon, who qualified second in his heat, while his US team-mate Maurice Mitchell also went through with a time of 20.54 seconds to win his heat.

Spearmon is bidding to pul behind him the disappointment of the Beijing 2008 final when he was disqualified from the bronze medal position for running out of his lane.

Boll stormed to the 100m gold medal on Sunday in an Olympic record 9.63 seconds, the second fastest time in history, as he banished any doubts about his form following an inconsistent season.