By Mitch Phillips

RIO DE JANEIRO (Reuters) - Olympic athletics got off to an astonishing start on Friday when Ethiopia's Almaz Ayana smashed a 23-year-old world record to win the greatest-ever women's 10,000 meters and then had to deny suggestions that her performance was fueled by drugs.

The world 5,000 meters champion, running only her second 10,000 meters, ripped the field apart to finish in 29 minutes 17.45 seconds, an incredible 14 seconds inside the previously untouchable 29:31.78 set by China's Wang Junxia in 1993.

Kenya's world 10,000 meters champion Vivian Cheruiyot took silver and though she was far behind, her time of 29:32.53 was still the third-fastest ever run. Ethiopian Tirunesh Dibaba, the double defending Olympic champion, took bronze.

No woman had gone under 30 minutes in the last seven years, but the first four all did on Friday, and even though the field was spread all over the track, the first 13 finishers ran the best time of their lives, including five national records.

After a bleak year of doping and corruption controversies it should have been an uplifting start to 10 days of athletics but, such was the magnitude of victory, Ayala was immediately forced to deny using performance-enhancing drugs.

"My doping is my training, my doping is Jesus. I am crystal clear," she said through an interpreter.

Sarah Lahti, who finished 12th in a Swedish record having taken 26 seconds off her own best, questioned Ayala's performance while marathon world record holder Paula Radcliffe said in commentary for the BBC: "I'm not sure that I can understand that.

"When I saw the world record set in 1993, I couldn't believe what I was seeing. And Ayana has absolutely blitzed that time."

Doping remained on the agenda away from the track too as Bulgarian Silvia Danekova's positive test for EPO was confirmed.

The 33-year-old, who was due to compete in the women's 3000 meters steeplechase on Monday, denied taking any drugs and blamed her test on her country's links with Russia.

"I feel robbed emotionally," she said. "But we’re coming from the east, we’re too close to Russia."

Virtually all of Russia's track and field team have been excluded from the Rio Games following revelations of state-backed doping.

Kenya's sprint coach John Anzrah was told he could face criminal charges after he was sent home for posing as an athlete in a dope test.

The country's athletics manager Michael Rotich has already been sent home but he was suspended by the International Association of Athletics Federation (IAAF)'s ethics commission on Friday following allegations of corrupt practices surrounding anti-doping.


The disappointing aspect of the opening morning's action was the sparse crowd to witness the fireworks.

There were only a scattering of fans to see the opening events, men's discus qualifying and heptathlon hurdles, though the numbers swelled in time for the 10,000 meters.

Games spokesman Mario Andrada said that 58 percent of tickets had been sold for the session, though only around 25 percent of seats looked occupied.

"We are not disappointed," he said. "We understand without local heroes and athletes some of the local public takes longer to fall in love with track and field but the fact that they can see Usain Bolt and iconic athletes will help."

Briton Jess Ennis-Hill got off to a good start in the defense of her heptathlon title with an impressive 12.84 seconds 100 meters hurdles on a wet track - blue for the first time at the Olympics.

However, she was outshone by compatriot Katerina Johnson-Thompson, who cleared a British high jump record of 1.98 meters to lead after two events.

With Dibaba missing out in the 10,000 meters, the way is now clear for Valerie Adams to become the first woman to win three successive athletics golds and she needed only one throw of 19.74 to lead the qualifiers for the shot put final scheduled for later on Friday.

The other gold medal up for grabs on day one is in the men's 20 km walk.

(Editing by Ed Osmond and Meredith Mazzilli)