Marisa de Aniceto, of France, seventh after five events, seized the heptathlon overall lead going in to the final event, after a 43.72m javelin throw.
In contrast, Jessica Ennis, from Britain, the competition leader since the first event on Saturday morning slumped back to sixth place after scoring just 392pts in the javelin with her 25.52m best effort.
In second place now is Brazil's Jailma Sales de Lima. After outstanding high jump and long jump scores, the Brazilian threw the javelin 36.18m for 594pts and a six-event total of 4539. De Aniceto, after scoring 739 in the javelin, has totalled 4584.
Sarah Kern, long-time second placer, in still just in the medal positions, scoring 537pts for her 33.20m javelin throw. The German has a total of 4508 going into her strongest event, the 800m, where Kern boasts a 2min 11sec PB.
With Gayle Hunter, from the United States, holding firm in fourth with her 33.11m javelin throw for 536pts and a total of 4487, and Yuliya Tarasova managing 34.27m (558pts) with her final throw for 4469 and fifth, Ennis is behind her on 4463.