Ethiopian distance runner Almaz Ayana smashed a 23-year-old world record to claim gold in the 10,000m as the Olympic athletics competition got off to a dramatic start on Friday.

Ayana, 24, left her rivals trailing as she finished in 29min 17.45sec, slicing nearly 14 seconds off the previous world best of 29:31.78 set by China's Wang Junxia in 1993 during the era of notorious coach Ma Junren.

Vivian Cheruiyot of Kenya took silver in a new national record of 29:32.53 while defending champion Tirunesh Dibaba won bronze in a personal best 29:42.56.

Yet the astounding nature of Ayana's victory immediately raised eyebrows in the athletics world. 
Marathon world record holder Paula Radcliffe was among the first to question Ayana's performance while Sweden's Sarah Lahti, who finished 12th, more than two minutes behind, was also sceptical.

"I do not really believe that she is 100 percent," Lahti was quoted by Swedish media as saying. "There is doubt." 

Yet a smiling Ayana was unruffled when asked to comment on suggestions that her performance might not be all that it seemed.

"I praise the lord, the lord gives me everything," she said through an interpreter. "My doping is my training, my doping is Jesus -- otherwise I'm crystal clear."

Ayana's win comes in a troubled year for Ethiopian athletics. 

The International Association of Athletics Federations in March placed the country in "critical care" with four other nations over failures in their anti-doping regimes. 

In other early action Friday, Kenya's reigning Olympic 800m champion David Rudisha cruised through the first round as he bids to defend his two-lap title.
Rudisha posted the fastest qualifying time of 1:45.09sec and will be joined in the semi-finals by a host of favourites including Djibouti's Ayanleh Souleiman, Bosnian Amel Tuka, Poland's Adam Kszcot and American Boris Berian.

"It was good," said Rudisha. "I'm in good form, there's no doubt about that. I'm very confident because I'm finding my finishing power in the last 100m, so I think I'm in a position to control my races again."

British heptathlon star Jessica Ennis-Hill also made a smooth start to the defence of her Olympic crown, sitting in third place after the opening two events of the gruelling discipline.

Ennis-Hill landed an early psychological blow on Canada's Brianne Theisen-Eaton with an impressive 100m hurdles victory. 

In blustery, overcast conditions, Ennis-Hill produced a blemish-free performance to win her race in 12.84sec. It was her third fastest time since winning in London.
Ennis-Hill's run earned her 1,149 points, putting her into the early lead of the seven-discipline event.

However, Ennis-Hill saw her lead whittled away in the high jump despite landing a season's best of 1.89m, the highest she has jumped since the London Games.

Belgium's Nafi Thiam and Briton Katarina Johnson-Thompson both cleared a world heptathlon best of 1.98m.

Johnson-Thompson's effort saw her take the lead on 2,264 points, with Thiam in second (2,252) and Ennis-Hill third (2,242).

The competition continues later Friday with the final of the women's shot put, where New Zealand's Valerie Adams will aim to clinch a third consecutive shot put gold medal.

Source: AFP