Usain Bolt and Justin Gatlin resumed battle as the 200 metres got under way at the World Championships.

Two days on from riding to the rescue of his beleaguered sport, the Jamaican began his bid to add half-lap glory to his 100 metres crown.

Bolt's biggest rival once again is two-time drug cheat Gatlin and both cantered through to the World Championship semi-finals in Beijing,

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The former, looking to win a fourth successive 200m world crown, flew out of the blocks and won despite easing up all the way down the straight, while Gatlin cruised to victory in his heat.

"Everybody knows that it will mean a lot more - actually more than the 100m," Bolt said.

"I'm just trying to get through these rounds using as little energy as possible and then give it my best in the final."

The British duo of Danny Talbot and Zharnel Hughes also secured safe progress, with the latter winning his heat in 20.13 seconds despite running from a difficult lane.

"I want to get a medal here, but my focus right now is to get into the final," Anguilla-born Hughes said. "There's a lot of big rivals out there, but I am a big rival myself.

"I might be looking at people, but people are looking at me at the same time.

"I just have to go out there and run each guy like it's the final.

"Surprises are here. A lot of people have running fast on this track, so you never know what can happen."