Briton Mo Farah continued his impressive track form by claiming a hard-fought victory in the world 10,000m on Saturday, as Jamaican sprint star Usain Bolt cruised through his 100m heat.
Farah, who is attempting to replicate the double 5,000-10,000m gold he claimed at last year's London Olympics, had a slow race pace, American training partner Galen Rupp and his own definitive race-end kick to thank for his victory.
There was an all-too-familiar finish to the 25-lap race when Ethiopia's defending world champion Ibrahim Jeilan tried to edge past Farah on the final bend.
Two years ago in the Daegu worlds, Farah wilted into second behind the sprint-clever Ethiopian, but a season dedicated to honing his speed this time paid dividends.
"It was the perfect race for me," the Somali-born Farah said. "It was quite slow, and the important thing was to stay out of trouble."
With Jeilan and his three teammates plus a strong Kenyan line-up, Farah said he and Rupp, who both train in Oregon, Portland, with Alberto Salazar, had tried "to work together and to cover every move".
"Two years ago, almost exactly the same thing happened (around the final bend). It was important I had something left on the final lap."
Jeilan took silver and Kenyan Paul Tanui bronze, Rupp just missing out on the podium in fourth.
Track icon Bolt, within touching distance of equalling American sprint legend Carl Lewis' record of eight world gold medals, clocked an easy-going 10.07sec in his heat of the 100m, which featured neither American rival Tyson Gay nor Asafa Powell after both tested positive for banned substances.
The Jamaican saw teammate Yohan Blake claim victory in Daegu after his shock false start in the final, the one blip on his impressive CV, that includes Olympic gold in the 100m, 200m and 4x100m relay events in Beijing and London, and five world titles, as well as the 100 and 200m world records.
Bolt will be joined in Sunday's semi-finals by American rivals Justin Gatlin, the 2004 Olympic champion, London bronze medallist and double world champion in 2005, and Mike Rodgers, who have both served doping bans.
The duo were the only sprinters to clock sub-10sec times to serve notice that Bolt will not have it all his own way.
"I am happy with my run," said Bolt, who survived a false start in his heat. "I took it easy as it was the first round. I just wanted to get my reaction and start right.
"The false start in my heat didn't affect me. I made that mistake in Daegu and now I'm staying focused."
The second gold on offer on the opening day of competition went to Tanui's teammate Edna Kiplagat, who became the first woman to retain the world marathon title.
The 33-year-old, who could only finish 20th in the London Olympics last year, timed 2hr 25min 44sec to take gold ahead of long-time leader Valeria Straneo of Italy (2:25.58) while Japan's Kayoko Fukushi took bronze (2:27.45).
"I'm delighted I was able to defend my title successfully. I got confident I was going to win at the 40km mark when I upped my pace," Kiplagat said.
Olympic champion Tiki Gelana of Ethiopia never featured on her return to competition after being knocked over by a wheelchair competitor during this year's London Marathon.
Kiplagat, having allowed Straneo to set the pace, finally made the decisive move just after the 40km mark, and this time the Italian had no answer, contenting herself with second place.
In the decathlon, Olympic champion Ashton Eaton of the United States started well, clocking a leading 10.35sec in the 100m, a third-best 7.73m in the the long jump, and 14.39m in the shot put.
But the world record holder and silver medallist in Daegu dropped to fourth after a best in the high jump of 1.93m. Teammate Gunnar Nixon's 2.14m saw him soar into the lead, followed by German Michael Schrader.
Eaton duly retook the overnight lead with a 46.02sec in the 400m, leaving him on 4,502 points, just nine ahead of Nixon and Schrader a further 66 points adrift.
"Before the 400m, my coach said to me: 'Wake up! It's the world championships. Come one, go into the lead for the second day'. And I did it. Now I feel some spark for Sunday," said Eaton.
Reigning double world champion Trey Hardee, in fifth after three events, failed to register a height in the high jump for a disappointing end to his campaign.
Sunday's second day of action features the 110m hurdles, discus throw, pole vault, javelin and the 1500m.