Jessica Ennis-Hill was on the brink of adding world heptathlon gold to her Olympic title on Sunday, as Spain's Miguel Angel Lopez broke Chinese hearts in the men's 20km walk.
Ennis-Hill, making her return to major competition with some panache after giving birth last year and battling a host of niggling injuries, enjoyed a 30-point overnight lead on British teammate Katarina Johnson-Thompson.
But there was drama in the first of three events when an astonishing show of bravado by Johnson-Thompson spectatularly backfired as she fouled out with all three efforts in the long jump, her strongest discipline.
The British team initially protested but withdrew their appeal after viewing the evidence and accepting that her final jump was indeed a foul.
That left Ennis-Hall atop the standings on 5706 points after she leapt 6.43m in the long jump and threw a best of 42.51m in the javelin with only the 800m to be raced.
Dutchwoman Nadine Broersen was second on 5620pts, with Canada's Brianne Theisen Eaton third (5612).
Sunday's action had kicked off with the men's 20km race walk, Angel Lopez reeling in Olympic bronze medallist and home hope Wang Zhen, who had looked set to claim the host country's first gold medal in Beijing after bursting clear at the 13km mark.
"The course was difficult and complicated, plus the heat. My last 200m were an incredible sensation -- I remembered all the people who have helped me," said the European champion.
Angel Lopez timed a personal best of 1hr 19min 14sec, Wang taking silver (1:19:29) and Canada's Benjamin Thorne claiming bronze in a national record of 1:19:57.
Japan's world record holder Yusuke Suzuki failed to finish, the hot gold medal favourite pulling out just after the halfway point in clear discomfort, blaming his problem on a pelvic injury.
Round one of the women's 100m saw all the usual favourites progress to the Monday's semi-final.
Jamaica's double Olympic champion Shelly-Ann Fraser-Pryce began her quest to win an unprecedented third sprint title with a new hair-do.
Her long mane braided and bright green, the petite Jamaican also boasted a garland of yellow flowers as she ploughed through the line in 10.88sec, the joint fastest qualifying along with American Tori Bowie.
"I was able to refocus after the false start, to focus on what is important," she said.
"Winning a third world title? Well every championship is different, this is a new championship. Today is just about getting through the rounds."