Jessica Ennis-Hill is on course for World Championship gold after Katarina Johnson-Thompson's challenge collapsed in agonising fashion.
Saturday proved a fascinating battle between master and apprentice, resulting in the British pair occupying the top two spots overnight.
The victor was only expected to become clear in the final heptathlon event on Sunday evening, yet Johnson-Thompson's disastrous long jump ruled her out of contention.
Ennis-Hill's season best effort of 6.43 metres gave her a comfortable cushion at the top of the overall standings, which remained solid after throwing 42.51m in the javelin.
It puts the London 2012 champion on the cusp of gold with just the 800m to go, boasting an 86-point cushion - the equivalent to approximately six seconds - over Holland's Nadine Broersen in second.
Johnson-Thompson, by contrast, ended a galling morning session in 29th place overall.
The 22-year-old started the day 80 points behind Ennis-Hill and was expected to wrestle away the heptathlon lead given her prowess in the long jump.
However, she ended the session 1,123 behind her compatriot after failing to record a distance, with the third red flag particularly exasperating.
It would have been the event's biggest distance was it not chalked off, with officials deeming Johnson-Thompson to have left the slightest imprint on the plasticine.
After several minutes of discussions, and despite her remonstrations, it was ruled an illegal effort - a decision British Athletics appealed, only to later withdraw it after accepting it was a foul.
It left Johnson-Thompson visibly shell-shocked, although she continued in the javelin and produced a best of 39.52m.
There were questions as to why she carried on given she has the long jump on Thursday, but British Athletics confirmed rules state there would have be a medical reason to withdraw and medical confirmation she could compete again.
Johnson-Thompson's frustration was one of few negatives for Britain on the second morning of competition, with team captain Martyn Rooney leading by example.
Having initially been omitted from the individual 400m, the 28-year-old proved his worth with a personal best of 44.45 seconds - almost a second faster than his season best.
The Bird's Nest had witnessed Rooney's previous PB at the 2008 Olympics, but it was not enough to secure automatic qualification, progressing instead as the fastest loser.
"The basis of my appeal was that I am a championship performer," he said. "But I have to make the final yet and then I'll be vindicated.
"For now, I need to come back and do it all again, and maybe even better."
Rabah Yousif secured automatic progression in the 400m but Jarryd Dunn exited, while Asha Philip made it through the women's 100m heats.
Eilidh Child and Meghan Beesley secured safe passage to the 400m hurdles semi-finals, with the latter finishing her heat third with a personal best of 54.52secs.
"I'm really happy," Beesley said. "I'll probably be thinking about it in a bit, but I'm so tired right now. Personal bests hurt."
Earlier in the day, Tom Bosworth came 25th in the 20km race walk in a time of one hour 23 mins 58 secs.