Budapest: The United States women's 4x400 metres relay team, who have won seven of the last eight World Championships and the last seven Olympic golds, were disqualified from Saturday's semifinals after a botched baton changeover.
The US were trailing Britain after three legs when Alexis Holmes initially failed to collect the baton from Quanera Hayes and by the time she got hold of it she appeared to have gone beyond the "blue box".
The US recovered to finish second behind the British in the heat but were marked as disqualified.
Jamaica and Canada were the fastest into Sunday's final.
The similarly dominant US men, who have won eight of the last nine world titles and four of the last five Olympics, also had a stutter as they were pushed all the way in the first heat by India.
Justin Robinson brought them home in 2:58.47 but only after fighting off a final bend challenge by Rajesh Ramesh that helped his team to an Asian record 2:59.05 - the first time they have cracked three minutes.
Britain snatched the third automatic place from Botswana by eight thousandths of a second but the Africans went through comfortably as their fastest loser time was quicker than the winners of the second semi.
Jamaica, perennial global silver medallists in recent years, won the second heat in 2:59.82, with fast-finishing France and Italy following them through. Fifth-placed Belgium, bronze medallists in the last two worlds, did not make it.
