By Aimee Lewis BBC Sport in Moscow
Olympic champion Usain Bolt defended his 200m title with ease and took his tally of World Championships gold medals to seven.
The Jamaican set a world leading time of 19.66 seconds to secure his third successive world title in the event.
Bolt’s compatriot Warren Weir clinched silver with a personal best 19.79 while America’s Curtis Mitchell (20.04) took bronze by a hundredth of a second.
Britain’s Adam Gemili, 19, dipped home in fifth, clocking 20.08.
“The 100m is for the fans, and for the show as the fastest man in the world, but for me it means more to come here and defend my 200 title,” Bolt said.
“When I entered the straight, I felt tired; my legs felt a little heavy. And my coach told me not to push too hard if it was possible, so I backed off a little.”
Gemili, who has made exceptional progress since taking up the sport a year and a half ago, did not look overawed in his first major championship final as a senior.
“What an experience this whole championships has been for me,” the former footballer told BBC Sport.
“There are no words to describe how I’m feeling. I knew I would be in the mix if I executed my race. I didn’t execute it as well as I could have, but I still have a lot of people to thank. I’m very lucky and I’m really happy.”
The Blackheath and Bromley athlete qualified second-fastest for the final after lowering his personal best in the semi-finals to 19.98, becoming only the second Briton to dip under 20 seconds.
Gemili was smiling broadly on the start line and the teenager, with Bolt on his inside, came out of the bend strongly and finished four hundredths of a second outside the top three.
Neither Gemili nor the other finalists could end Bolt’s reign. The defending champion, who has now completed his second Olympic and world sprint double, led coming into the bend and from then on overpowered them.
As the finishing line neared, the six-time Olympic champion eased off and had time to look over his shoulder to check his team-mate Weir had grabbed second.
Bolt’s winning time was nearly five tenths slower than the world record time of 19.19 he set in Berlin, and the slowest of his gold-medal wins over the distance.
But with Tyson Gay absent through suspension and compatriot Yohan Blake injured, Bolt did not have to produce a vintage display to secure the result the vociferous sell-out crowd in the Luzhniki Stadium expected.
By the time the world record holder celebrates his 27th birthday on Wednesday, he could see his name alongside Americans Carl Lewis, Michael Johnson and Allyson Felix as the most decorated gold medallist in the championships’ history.
The speed of Bolt’s progress to the top of that list of high achievers depends on Sunday’s 4x100m sprint relay final.
Should the Jamaicans repeat their gold medal-winning exploits of London 2012, the man from Kingston will on Sunday evening be the owner of eight gold World Championship medals, equalling the American trio’s record of eight.
With two silvers also in his collection, it would be Bolt’s 10th medal in all, bringing him level with Lewis and Felix.
Elsewhere, there were two bronze medals for Britain on the eighth day of competition thanks to Tiffany Porter in the women’s 110m hurdles and the women’s 4x400m relay team.
Porter could not hide her joy, skipping down the track and waving to the crowd, at becoming Britain’s first World Championship .
“With the hurdles anything can happen, but I believed in myself,” said the 25-year-old, who lowered her personal best by a hundredth of a second to 12.55.
“I was racing against some very talented ladies so I’m just really proud to have won a medal.”
Reigning Olympic champion Sally Pearson, who has been hindered by injuries this season, ran a season’s best 12.50 but had to settle for silver as America’s Brianna Rollins beat her to gold.
In the women’s 4x400m relay, Britain’s bronze gave Christine Ohuruogu her fifth major championship medal.
The quartet finished behind champions Russia, who set a world-leading time of three minutes 20.21 seconds to force the Americans to relinquish the crown they have held since 2005.
“We’ve been running together, contending for medals, since the indoor season. It’s a nice end to our 4x400m campaign,” said Ohuruogu, whose final lap 49.60 split was her best split time in the event.