Beijing (AFP) - Eritrea claimed the first gold of the world championships when unheralded teenager Ghirmay Ghebreslassie stormed to a shock victory in the men's marathon on Saturday.
The opening day of the worlds in Beijing will later see sprint rivals Usain Bolt and Justin Gatlin square up in the 100m heats while Mo Farah takes a shot at 10,000m history.
After a build-up marked by controversies over doping, competition finally got off to an early start when Uganda's Stephen Kiprotich defended his marathon title.
But in hot, clear conditions, Kiprotich could only finish sixth as 19-year-old Ghebreslassie took the lead from Lesotho's Tsepo Ramonene Mathibelle on the 36km mark and saw off pressure from Ethiopian Yemane Tsegay for a memorable win in 2hr 12min 27sec.
"I am so proud of this victory. This is my first gold medal in my first marathon championship," said the Eritrean, crowned the youngest ever world marathon winner in just his fourth race.
"It's a very special thing for me. It gives me motivations to continue to work hard. My medal is the first gold medal in Eritrean history."
Eritrea had previously only ever claimed one medal -- a silver by Tadese Zersenay's silver in the 10,000m in the 2009 worlds in Berlin.
- No drama for Dibaba, Rudisha -
There were no dramas for Ethiopian Genzebe Dibaba or Kenyan David Rudisha in heats for the women's 1500m and men's 800m respectively.
Dibaba, who is hunting a 1500-5000m double having recently set a new world record in the shorter race in Monaco, coasted her heat in a fastest time of 4:02.59.
"This is a special championships in a special city because my sister (Tirunesh) won two golds here" at the 2008 Beijing Olympics, Dibaba said.
"So my main goal is to get two gold medals too. I know I can run very fast and I am ready to run faster in the following rounds but my main goal is just a medal."
Rudisha likewise had no problems, along with Botswanan rival Nijel Amos, easily coming through his heat in 1:48.31.
"I have qualified and now I'm looking forward to the final," said Rudisha, who has overcome a thigh injury earlier this season.
A mere 30 points separated British duo Jessica Ennis-Hall and Katarina Johnson-Thompson at the top of the leaderboard in the women's heptathlon.
They re-group to go in the shot put and 200m in the evening session, with main rival Brianne Theisen Eaton of Canada sitting fifth, 57 points adrift.
- Gatlin, Bolt to make bow -
Those later events will take place against a backdrop of doping intrigue, especially when twice-banned Gatlin runs in the first round of the 100m, with the semi-final and final scheduled for Sunday.
Gatlin, 33, has the world's leading time of 9.74sec and is riding a winning streak of 27 straight races, stretching back to August 2013 and is considered favourite to dethrone Bolt.
Bolt has recovered from pelvic joint pain to twice run 9.87 in London last month, and will be up against it in his bid to defend his double sprint titles, the towering Jamaican having won nine of 10 individual sprint titles on offer since the 2008 Olympics.
Another runner seeking a historic victory will be Farah, the 5,000m and 10,000m world and Olympic champion.
Should Farah win the 10,000m in the Chinese capital, he will have strung together an unprecedented six consecutive global track distance titles, with a chance to make it seven in the 5,000m.
Farah will undoubtedly face a tough challenge from the Kenyan and Ethiopian trios, with US training partner Galen Rupp, fastest in the world last year and silver medallist behind the Briton at the 2012 Olympics, also expected to be in the mix.
One notable absentee from Saturday's action, featuring three medal events, will be New Zealand's four-time world champion Valerie Adams, who misses the women's shot put after complicated double surgery on her shoulder and elbow.
In the Kiwi's absence, the world leader from Germany, Christina Schwanitz, is favourite, while home hopes lie with Olympic and two-time world bronze medallist Gong Lijiao.