Champion knows the end is near, but until then he'll keep on handing out lessons to over-optimistic rivals.

As it turned out, the greatest threat to Usain Bolt in the 200 metres came not from Justin Gatlin but from a Segway scooter.

Moments after the finest sprinter in history had swept to victory in 19.55s - his fastest time over the distance since his win at the London Olympics - his priceless legs were taken out from underneath him by a photographer's inept driving.

While Bolt laughed off the alarming incident at the world championship final in Beijing, springing away with a backward roll, he could have been gravely injured. It was the type of drama he least expected as he embarked on a lap of honour, besieged by hordes of Chinese fans craving selfies.

He wanted to savour every last drop of adulation, having vanquished Gatlin with a second magnificent display in seven days.

Advertisement

Until, that is, the errant cameraman arrived, hitting a metal strut with his scooter and veering straight into the back of the newly minted world champion and upending him.

Bolt, as is his wont, took the indignity in good humour, even checking to see that his assailant was unhurt. Not that he was entirely unruffled. "He tried to kill me!" he said, with a grin. "It was like, 'You are winning too much - take him out '."

There was another conspiracy theory to concoct.

"The rumour I'm trying to start is that Justin Gatlin paid him off," Bolt said, within earshot of the American. "I want my money back," Gatlin replied, at least partly in jest.

They could afford, after all the "good versus evil" caricatures of the past seven days, to indulge in some playful joshing. For the much-awaited rematch was not even close.

Bolt had Gatlin beaten early at the Bird's Nest, running a wonderful bend to streak clear of the field. Ultimately, it was a statement to which Gatlin had no answer. Instead, he succumbed to the type of late stumble that sank his 100m chances, losing form and technique as his nemesis prevailed by almost two tenths of a second.

Everyone wanted a piece of Bolt after this triumph. One enterprising teenager in the crowd jumped over the barrier and stole his running spikes, only to be intercepted by a ring of security guards as he ran off.

How much more of this madness can Bolt, consummate showman that he is, take as his wonderful career draws towards a close?

Advertisement

Not a great deal, if we are to believe the 29-year-old's claim that he is only "50-50" to compete at the next world championships in London. His sponsor, Puma, wants him to continue until 2017, but Bolt indicated that next year's Olympics in Rio would be a more fitting stage on which to bow out.

That debate can wait, when there are still performances such as this to savour. Gatlin went into this competition unbeaten in 27 races and with the five fastest 100m and two quickest 200m times of the year.

But Bolt, who has extended his winning run over Gatlin to 10 years over 200m, still waltzed off with the sprint double once more.

Not only was it Bolt's fourth consecutive world title in the 200m, it was also his 10th world championship gold overall. An apt achievement, he felt, to throw back in the faces of those who had doubted him.

"It means a lot to me," he said. "I'm happy, especially when people have been saying I would lose. As long as my coach is confident, I am super-confident. There was never a doubt that I would win this one. I am No 1, and I will continue running fast."

So fast, indeed, that Bolt could afford to ease up over the final 30m and still run the 10th best 200m of all time.

He reflected that he could have been in the region of 19.3 if he had run hard through the finish but, such was his flawless intuition about whether or not he was on world-record pace, he shifted down a gear so as not to tire himself for the sprint relay.

The emphasis with which he slapped his chest as he crossed the line showed how much he cherished another glory in his favourite event.

The margin of this win, with Gatlin a remote second in 19.74, also emboldened Bolt to try a little trash-talk.

"I really celebrated, because Gatlin said earlier in the week that he was going to bring out something special for the 200," he said. "I thought, 'Yo, you don't talk about my 200 like that'. So I had to prove to him that I am No 1."

Zharnel Hughes, the Anguillan-born Briton who had harboured hopes of a bronze, was fifth in 20.02. Bolt, his idol and his training partner at the Racers Track Club in Kingston, Jamaica, had delivered another masterclass.

"People were saying that he wasn't in shape, but he is a phenomenal athlete," Hughes said. "He is a legend."

Bolt, even as he contemplates retirement, is an icon whose preciousness to his sport is incalculable. If only somebody had told that wayward cameraman.