East Londoner Perri Shakes-Drayton failed to make it through to the 400 metres hurdles final after an appeal from a rival.
At first she failed to progress as a fastest loser in the semi-final, then was sent through when Denisa Rosolova was disqualified for a lane infringement and finally was out again as the Czech team successfully appealed.
Shakes-Drayton experienced contrasting emotions as disappointment turned to delight and then to despair.
The home favourite, joint second in the world rankings, clocked 55.19s to finish third in her heat and it looked like that time would not be good enough.
The initial disqualification of Rosolova was followed by a successful Czech appeal and when the British team asked the track referee to look again at the incident he declined.
Speaking before she knew the final outcome, Shakes-Drayton admitted the whole situation was "emotional".
Eilidh Child went out, finishing seventh in 56.03.
Child said: "My stride pattern didn't go to plan. I am gutted. I have come off thinking I could have done a lot better."