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Usain Bolt blew away any lingering doubts about his form as he cruised through Saturday's 100m heats at the World Championships in silky-smooth fashion.

Sporting a new-look goatee beard, the world record holder switched off at 70 metres yet still clocked 10.10 seconds into a headwind of -0.7m/s.

It completed an impressive showing from the four Jamaicans on display, with Yohan Blake, Michael Frater and Nesta Carter all winning their heats comfortably.

Britain's Dwain Chambers and Harry Aikines-Aryeetey both went through to Sunday's second round as automatic qualifiers, with Marlon Devonish joining them as a fastest loser.

Bolt said: "I got a great start. I feel so happy. I've been working on it so hard throughout the whole season. I got it when it's necessary so I'm happy. A lot of work has gone into it.

"People may think that I can run another fast time but I'm just saying I'm here to defend my title and show the world, 'Look, I'm still the best'."

Reigning world and Olympic champion Bolt has been far from his best in Diamond League competition this summer, but he underlined his status as red-hot favourite to retain the title he won in such blistering fashion in Berlin two years ago with a dominant display of relaxed running.

Chambers, out in lane eight, showed his experience by coming through second in 10.28, 12 years after winning World bronze.

Blake, seen by many as the man most likely to push his compatriot Bolt in the absence through injury of Tyson Gay and Asafa Powell, won the fourth heat in 10.12 secs while Carter - drafted into the Jamaican team late on after the positive drugs test for Steve Mullings - won his at a cruise in 10.26 secs.

European 100m and 200m champion Christophe Lemaitre also looked in smooth form as he led home the 2005 champion Justin Gatlin - making his first appearance at a global championships since returning from a four-year doping ban - in the third heat.

After the opening ceremony's fireworks had lit up the vast stadium earlier in the evening, Vivian Cheruiyot led home a Kenyan one-two-three-four in the first track final of the championships, the women's 10,000m.

Linet Masai had led a diminishing front group through 8000m and 9000m before Cheruiyot pulled away with Sally Kipyego in close pursuit at the bell and then kicked again with 150m left to go away for the gold, Priscah Cherono completing the procession in fourth.

Earlier in the day Edna Kiplagat had led home a similar sweep in the marathon, meaning that Kenya won all six medals on offer on day one.

Saturday's morning session began well for Britain, Barbara Parker making it through the 3,000m steeplechase heats and Andrew Osagie qualifying comfortably from his 800m heat, although European silver medallist Michael Rimmer, struggling with injury, went out.

Steve Lewis also qualified for Monday's pole vault final as his training partner, Australia's reigning champion Steve Hooker, crashed out after three failures at 5.50 metres.