USA's Francena McCorory in the 4x400m (© Getty Images)
There can be many a slip twixt cup and lip when it comes to relay racing but only a dropped baton or lane infringement seems likely to stop the Americas team.
Their quartet features four of the six fastest women in the world this year: world indoor champion Francena McCorory of the US plus the Jamaican trio Novlene Williams Mills, Stephenie Ann McPherson and Christine Day.
Their toughest competition should come from Europe, whose team includes the three medallists from the individual 400m at the European Championships: Libania Grenot, Olha Zemlyak and Indira Terrero.
Simon Turnbull for the IAAF
