Great Britain will miss the men's Olympic 4x100m relay final after being disqualified in their semi-final.
The team finished second but the final handover between Daniel Talbot and Adam Gemili, 18, was not completed in time.
Gemili said: "Maybe I went early or too hard. It's disappointing as we could have been in contention in the final."
"It looked like Gemili went a little bit early. There could have been a situation where Adam was just so amped up and excited by this crowd, this moment and this opportunity that he was running a little bit faster than the mark was made for."
Favourites Jamaica rested Usain Bolt but still won heat one, while, in the second, the United States recorded the fastest overall qualification time.
Britain, who won this event at the 2004 Games in Athens, were disqualified in Beijing four years ago and have now made a mess of baton changes in five of the last six major championships.
Talbot said: "I don't know what happened. I just couldn't catch Adam. I'm really gutted and it's devastating."
Christian Malcolm, who ran the first leg for Britain, described the outcome as "unfortunate". He added: "It's one of those things that happens but it's a fantastic performance to run the time we did. Daniel has come in at the last moment. This is a big stadium and it can be overwhelming."