Why the whole world is talking about Usain Bolt's final ever race.

Convicted drug cheat Justin Gatlin has rained on Usain Bolt’s farewell parade by beating the Jamaican super sprinter in the men’s 100m final at the athletics world championships in London.

Gatlin, the 35-year-old American who has served two doping bans, claimed the gold in 9.92 seconds, as Bolt was made to pay a heavy price for another tardy start.

Fastest qualifier Christian Coleman from the US was second in 9.94 and a fast-finishing Bolt was third in 9.95.

It was the final individual race for the 30-year-old Jamaican at an Olympics or world championships, although he will get one more shot at a title in London in the 4x100m relay next weekend.

Gatlin was booed before each of his three 100m races by the capacity crowd at the London Olympic Stadium and again when his name flashed up on the scoreboard as the winner.

But Bolt was quick to embrace the American at the finish line.

“He is a great competitor,” said Bolt.

“You have to be at your best against him. I really appreciate competing against him and he is a good person.”

Gatlin said he tuned out the approbation from the grandstands.

“The people who love me are here cheering for me and cheering at home,” he said.

“It is Bolt’s last race and he’s the man so it’s not about beating him.

“I have had many victories and many defeats down the years, he’s pushed and inspired me to be the athlete I am today.

” .. the first thing (Bolt) did was congratulate me and say that I didn’t deserve the boos.

“He is an inspiration.”

Apart from a false start in the world 100m final six years ago in Daegu which gifted the title to countryman Yohan Blake, Bolt had been unbeaten in 100m and 200m finals at global championships dating back to 2008.

Gatlin had gone closer than anyone to ending that streak at the 2015 world titles in Beijing, when he was edged out by one hundredth of a second in the 100m decider.

On Saturday night, the 2004 Olympic champ and 2005 world titleholder finally got his man.

Bolt paid a heavy price for again being sluggish out of the blocks in a race where just three hundredths of a second separated the medallists.

"My start is killing me," he said.

"Normally it gets better during the rounds but it didn't come together. And that is what killed me. I felt it was there.

"It was rough and I was a little bit stressed.

"But I came out like at any other championships and did my best."

Gatlin's career has been plagued by doping controversies.

In 2001 at the US junior championships, he failed a doping test for amphetamines found in prescribed medication he had been taking since a child for Attention Deficit Disorder. He was given an early reinstatement by the International Association of Athletics Federations (IAAF) the following year but warned a second violation would lead to a life ban.

In April 2006, Gatlin then tested positive for male sex hormone testosterone and its precursors at Kansas Relays. The details of test did not emerge until Gatlin issued a statement on July 29, 2006. He denied any wrongdoing and his coach claimed the positive test was the result of massage cream containing testosterone being rubbed into his buttocks.

At the time, he accepted an initial eight-year suspension, avoiding a lifetime ban in exchange for his cooperation with the doping authorities, and because of the "exceptional circumstances" surrounding his first positive drug test. The ban was reduced to four years by an arbitration panel in December, 2007.

In 2010, he returned to the sport.