The US men's 4 x100 meters relay team failed to qualify for the Olympic final after dropping the baton in their heat on Thursday.
Victory seemed a formality as Darvis Patton approached Tyson Gay on the final changeover but the pair made a mess of it and the baton tumbled to the floor.
The US were chasing their 16th gold medal in the 4x100m relay and were hoping to make up for Athens four years ago when they were surprisingly beaten by Britain.
Gay has endured a miserable Olympics after also failing to reach the 100 meters final.
Medal prospects Nigeria also failed to get the baton round along with South Africa and Poland.