Usain Bolt answered questions over his fitness ahead of the World Championships with a season's best of 9.87 seconds in the 100 metres courtesy a workmanlike performance at the London Anniversary Games on Friday.

With just under a month to go before he defends his world 100 and 200 titles in Beijing, the Jamaican showed he had recovered from a pelvic injury that has disrupted his season, although he was left with plenty to ponder in the rain-lashed capital.

The world's fastest man shook off the rust from his layoff -- this was his first 100 for over three months and first competitive race since mid-June -- to win his heat and the final in the same time, putting him equal sixth in the world this year.

But he had to eat up the ground in the second half of both races, winning the final by three-hundredths of a second ahead of American Mike Rodgers (9.90) and fellow Jamaican Kemar Bailey-Cole (9.92).

"In the final I got a really bad start, I kind of lost focus but I got it back," Bolt told reporters after a routine lap of honour by his own showman standards. "I know I could have gone faster if I had just got my start."

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Asked about his fitness, Bolt added: "I'm good. I may go to see the doctor to make sure everything is fine but I'm feeling good. I'm still number one, I've never been number two."

Bolt gave Mo Farah a hug as he left the track, leaving the Briton to take centrestage and conjure memories of his 2012 Olympic triumphs in the same stadium.

Farah has been dogged by the doping allegations surrounding his coach Alberto Salazar but received a huge ovation before and after winning the 3,000 metres in 7:34.66, the fastest time in the world this year.

Farah, who has not been accused of any wrongdoing, imitated the 'Lightning Bolt' pose of the Jamaican and told reporters: "You can only do what you do best and that, for me, is running."

On a night when the soaking conditions made fast times difficult, American former world champion Jason Richardson took the 110 metres hurdles spoils in 13.19 seconds.

Olympic champion and world record holder American Aries Merritt could only finish fourth, while Cuban Orlando Ortega, the fastest in the world this year, was fifth.

Jasmin Stowers, who will not compete in Beijing after missing selection, led home an American 1-2-3 in the women's 100m hurdles, winning comfortably in 12.47 seconds ahead of Dawn Harper-Nelson (12.64) and world champion Brianna Rollins (12.65).

The grim conditions for competitors were underlined when the pole vault competition was postponed until Saturday.