LONDON - Usain Bolt stayed on track for an Olympic sprint double as he and Jamaican rival Yohan Blake eased into Thursday's final of the 200m with commanding runs in their semi-finals on Wednesday.

Blake strolled to victory in his heat in 20.01sec but eased up before the line, while 100m champion Bolt was imperious as he held off the field to win his race in 20.18sec, looking around all the way down the home straight.

"It was all about going through as easy as possible, that was the aim. I did pretty well so I am happy," Bolt said.

He said there was "no doubt whatsoever" that he would successfully defend the crown he won in Beijing four years ago.

"People always doubt the champion but I know what I can do so I never doubt myself. This is my favourite event so I am looking forward to it."

Churandy Martina of the Netherlands won the third semi-final in a time of 20.17sec, with a third Jamaican, Warren Weir, qualifying behind him.

Wallace Spearmon will be the only US athlete in the final after he finished second behind Blake in 20.02sec.

(AFP)