PHOTOS: Farah, Bolt ignite Day 1 of athletics world championships

Mo Farah and Usain Bolt ignited the first day of the athletics world championships on Saturday but the event was blighted by dire crowds and yet another high-profile doping scandal for a leading sprinter.

Despite hot and humid conditions Bolt barely broke sweat in his 100 metres heat as he sauntered into Sunday's semi-finals in 10.07 seconds.

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Organisers, whose claims to have sold 80 percent of seats for the August 10-18 championship look hopelessly optimistic, will hope a few more fans turn up for Sunday's showpiece final.

Only a few thousand were scattered around the vast 81,000-capacity Luzhniki Stadium even for Saturday's opening ceremony where Russian President Vladimir Putin officially opened the showpiece.

Those who were there were treated to a consummate performance by Briton's Olympic distance-double champion Farah in the 10,000 metres, while Kenya's Edna Kiplagat also produced a tactically astute run to retain the women's marathon.

Bolt starts as an unbackable favourite to add the 100m title to his Olympic double, partly due to the absence of fellow Jamaican Asafa Powell and American Tyson Gay, who have both failed drugs tests.

Leading Jamaican women sprinters Sherone Simpson and Veronica Campbell-Brown also tested positive in the lead-up to Moscow and on Saturday Kelly Anne Baptiste of Trinidad and Tobago, bronze medallist two years ago behind silver winner and former champion Campbell-Brown, joined them.

Trinidad officials confirmed that Baptiste and team mate Semoy Hackett had withdrawn from the championships, though news of her positive test came only from the Trinidad Express newspaper.

With every doping case that rocks the sport, Bolt's value increases, though there was little showboating on Saturday as the Jamaican went about his business with a serious look.

A false start in the lane next to him, sparking memories of his final disqualification two years ago, did not shake his concentration.

"I just wanted to get my reaction and start right," he said. "The false start didn't affect me - I made that mistake in Daegu and now I'm staying focussed."

American duo Mike Rodgers and Justin Gatlin both dipped under 10 seconds to lead the qualifiers, with Peimeng Zhang also catching the eye with a Chinese record 10.04.

Two years ago Farah was agonisingly pipped on the line by Ethiopia's Ibrahim Jeilan in the world 10,000 final but he is a very different athlete now and though Jeilan pushed him all the way again on Saturday, the Somalia-born Briton always looked the winner.

Fully confident he could win any kind of race, he worked his way slowly through the field, survived one or two hairy stumbles as the elbows flew, before taking up the running 800 metres out.

Having recently broken the European record over 1500, his finishing speed was never in doubt and though Jeilan hung on gamely, Farah's fearsome last lap brought him home in 27:21.71 ahead of Jeilan and Kenya's Paul Tanui.

"I thought 'not again,'" said Farah, whose bulging eyed stare of horror as Jeilan swept past him in 2011 has become an enduring image of the sport.

"I was just digging in, digging in. It was important to have something left as I did not want to lose again.

"I kept looking across and you could see in my eyes, just making sure they didn't come after me."

Farah will now bid to complete the double-double by retaining his 5,000 title next week.

The first medals of the day were decided in the women's marathon, where 33-year-old Kiplagat, who led a Kenyan sweep in 2011, started steadily then patiently tracked surprise front-runner Valeria Straneo until the 40km mark.

She then broke clear to triumph in 2:25:44, leaving 37-year-old Italian to take silver ahead of Japan's Kayoko Fukushi.

Straneo, who had her spleen and gall bladder removed three years ago, was delighted with her silver and performed a cartwheel on the track after crossing the line. 

There was drama in the decathlon where double defending world champion Trey Hardee crashed out after no-heighting in the high jump.

Hardee, who triumphed in Berlin and Daegu and took Olympic silver last year, strained a hamstring and failed to clear 1.90.

Fellow American and Olympic champion Ashton Eaton's 47.02 seconds 400m was the fastest in 30 years of world championship decathlons and earned him a slender lead over 20-old compatriot Gunnar Nixon.

Britney Reese, Olympic long jump champion and winner of the last two world titles, cut it fine in qualifying as she scraped into the final in 12th and last place on countback with 6.57 metres, way down on her best of 7.25 set earlier this year.

The American will hope for a quick improvement when she returns for her final on Sunday, when the men's 100m showdown takes centre stage.

The decathlon is also decided and there are medals up for grabs in the women's 10,000 metres and women's discus.