Jessica Ennis was left with a mountain to climb to retain her pentathlon title at the World Indoor Championships in Istanbul.
Ennis led by 10 points after the 60 metre hurdles, high jump and shot on Friday morning, but then dropped to third following a sub-par performance in the long jump.
Jumps of 6.19m and 6.18m were followed by a foul in the final round to leave Ennis 93 points behind Ukraine's Olympic champion Nataliya Dobrynska - who won the long jump with 6.57m - with Austra Skujyte six points ahead of Ennis in second.
That left Ennis needing to beat Dobrynska by around seven seconds in the final event, the 800m - an unlikely scenario.
Russia's Tatyana Chernova, who took Ennis' world heptathlon title in Daegu last summer, was surprisingly down in fourth place, 165 points behind Ennis.
Ennis had made an ideal start with victory in the 60m hurdles in a time of 7.91 seconds - her second fastest ever - but was disappointed to clear only 1.87m in the high jump.
A personal best of 14.79m in the shot kept her in the lead after the morning session, but a poor long jump left the 26-year-old with an uphill battle to avoid a second straight defeat.
Away from the pentathlon, Britain's other defending champion safely advanced to the semi-finals of his event, Dwain Chambers winning his heat of the 60m in 6.65 seconds.
Chambers was the third fastest qualifier overall, just 0.01s behind Spain's Angel Rodriguez and American Justin Gatlin.
America-born hurdler Tiffany Porter also shrugged off the controversy over her selection as British team captain to win her heat of the 60m hurdles and reach the semi-finals.
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