RIO DE JANEIRO (AFP) - The United States' women's 4x100m relay team face a nerve-jangling time-trial to force their way into Friday's final after a dropped baton drama Thursday (Aug 18).
In an unusual move, the American quartet will re-run their race as a solo heat with the task of trying to beat eighth-fastest qualifiers China's time of 42.70sec.
China later responded to the US reprieve by filing a protest against the decision, officials confirmed.
The decision to give the defending Olympic champions another crack at reaching the final came after a tumultuous morning heat.
US star Allyson Felix was bumped by a Brazilian rival as she prepared to hand over to English Gardner, knocking her off balance and sending the baton tumbling to the floor.
At first glance it looked like another in a long line of US relay blunders in recent years.
The US women botched an exchange and dropped a baton in both the 2004 and 2008 Olympics.
But the US protested the latest apparent gaffe, citing the contact made with Felix, and the race referee handed them a reprieve.
"The referee examined the video of the race and agreed that the US runner was obstructed at the second exchange," a statement said.
The US team, which also includes Tianna Bartoletta and Morolake Akinosun, will have a re-run alone, in the same lane, at 7pm to attempt to qualify by time, the statement added.
An earlier statement said the time-trial would take place at 8pm.
Brazil, who had initially finished fourth, were disqualified.
The heat was won by Germany's quartet in 42.18sec ahead of Nigeria, Trinidad and Tobago, and Brazil.
In the other semi-final, Jamaica stormed to victory in 41.79sec.
The Jamaican women - including heavyweight veterans Veronica Campbell-Brown and Shelly-Ann Fraser-Pryce - were pushed all the way by Britain, who finished in 41.93sec.
Jamaica's newly-crowned 100m and 200m champion Elaine Thompson sat out the heat but will return for the final.
"We are putting things together well but we'll have to change a few things for the final," Campbell-Brown said.
"There will be some changes that you will see tomorrow, Elaine will definitely be on."
