​Mo Farah has backed Usain Bolt to beat Justin Gatlin in the 100 metres final at the World Championships.

Six-time Olympic gold medallist and reigning world champion Bolt will go head to head with Gatlin - who has twice been banned for doping - in track and field's blue-riband event at Beijing's Bird's Nest Stadium on Sunday.

American Gatlin is the fastest man in the world this year and clocked the quickest time of Saturday's 100m heats, with his 9.83 seconds comfortably better than Bolt's 9.96secs.

However, Farah - who won a sixth-straight global track distance gold by defending his 10,000m crown on Saturday - said a Gatlin triumph over Bolt would be difficult to see given the 33-year-old's history.

"I guess as an athlete, when I line up I wouldn't want to be able to see someone who's been banned or gone through that stuff and still be racing against you," commented the Briton.

When asked if he would watch the mouth-watering 100m final, Farah replied: "Yes I'm going to watch it. I think Bolt's got it."