Olympic Rings (File)
Rio de Janeiro - The United States women's 4x100 relay team dramatically crashed out of the Olympics here on Thursday.
The defending Olympic champions tumbled out in their opening heat after a bungled second baton changeover between Allyson Felix and English Gardner.
Replays of the exchange were inconclusive, although Felix appeared to stumble and grimace before she reached Gardner to hand over the baton.
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.