Mo Farah's bid to defend his double world distance titles almost came unstuck on Wednesday as he was tripped coming into the final 200 metres of his 5,000m heat.
Great Britain's Farah, who won 10,000m gold on Saturday, was in control of the race throughout but was clipped coming into the final bend, leaving him with a cut toe and causing him to stumble badly before correcting himself.
To gasps from the Bird's Nest crowd in Beijing, Farah relaunched himself to finish second behind Ethiopian winner Yomif Kejelcha, the world's fastest performer in 2015, who timed 13min 19.38sec in the hot morning sun.
Another Ethiopian, Hagos Gebrhiwet, won the first heat, clocking 13:45.00 to set up a mouth-watering clash in the final scheduled for 1130GMT on Saturday.
"It felt all right. I nearly went down -- again!" laughed Farah in reference to stumbling also in the 10,000m final.
"I hope it doesn't come a third time, that would be bad luck.
"Somebody just caught my legs. It's the way I run, I've got long strides so I don't blame anybody. It just happens. That's why sometimes I just have to be at the front or the back or stay on the outside."
The Somali-born 32-year-old said that victories in the heptathlon and men's long jump by Great Britain teammates Jessica Ennis-Hill and Greg Rutherford had not only eased the pressure on him but also highlighted an "amazing team spirit".
- 'Anything can happen' -
"It brings back 'super Saturday' with myself, Jess, Greg," he said, referring to the first night of action at the 2012 London Olympics when all three won gold.
Victory for Farah on Saturday would signify an unprecedented seventh successive win in the 5,000 or 10,000m at a world championships or Olympics stretching back to 2011.
Farah warned, however, that he would take nothing for granted given the strong field.
"You might be the favourite but anything can happen," he said.
"I think there are three or four guys who are capable. Three Ethiopians and two Kenyans in the final -- I don't know what's going to happen."
The third Ethiopian will be the experienced Imane Merga. Also progressing to the 15-man final will be Farah's training partner Galen Rupp of the United States.
The Kenyans comprise Caleb Ndiku, Isiah Koech and Edwin Soi, while there are two other Kenyan-born runners in the field representing new countries of allegiance -- Bahrain's Albert Rop and Turkey's Ali Kaya.
There will be another Briton in Tom Farrell, while Ryan Hill and Ben True make up the trio of Americans to complete the final line-up alongside Germany's Richard Ringer and Canada's Mohammed Ahmed.
- Bolt, Gatlin feature -
The evening session in Beijing Wednesday sees rivals Usain Bolt and Justin Gatlin race the semi-finals of the 200m, with the final scheduled for Thursday.
Bolt drew first blood in the battle with Gatlin, who has served two doping bans, when the towering Jamaican edged the American to the 100m title on Sunday.
Kirani James of Grenada will later bid to add world gold to his Olympic 400m title but in what is shaping as a thriller, he will be pushed hard by contenders including defending champion LaShawn Merritt.
Other finals on Wednesday include the women's pole vault, 400m hurdles and 3,000m steeplechase, as well as the men's javelin.
There will also be women's 200m heats, albeit missing 100m winner Shelly-Ann Fraser-Pryce and America's Allyson Felix, who both opted out, blowing the field wide open.
Much-decorated Jamaican Veronica Campbell-Brown could push for a golden swansong, although countrywoman Elaine Thompson, Nigeria's Commonwealth Games champion Blessing Okagbare and Dutch 100m silver medallist Dafne Schippers are expected to shine.