Monique Gladding and Stacie Powell have missed out on making it past the opening round of the women's 10m platform diving at the Aquatics Centre.
The British pair were agonisingly left in the two places below the 18-diver cut-off as Gladding finished 6.65 points below the cut.
The 31-year-old, who scored 301.45, battled back to qualify for her first Olympics following a freak accident during a meet in Russia 18 months ago.
Gladding hit her head on the 10-metre tower and plummeted unconscious into the water and had to be rescued from the bottom of the pool, with her husband and coach Steve Gladding watching on in horror.
The City of Sheffield diver was left with a large scar across the top of her scalp and later revealed she had been seconds from death.
Despite that she had enjoyed the best 12 months of her decade-long career on the platform to qualify for her first Games, albeit after fending off an appeal from Tonia Couch.
Couch finished above Gladding at June's national trials, but British Diving performance director Alexei Evangulov opted to select the veteran, with Couch ordered to concentrate on the synchro.
Powell, who is studying for a PhD in astrophysics at the University of Cambridge, had scored a British record score of 376.05 at the trials in Sheffield to book her Games place, but a total of 287.30 on Wednesday left in 20th place.
Both are reserves for Thursday morning's semi-final in the unlikely event of injury or illness to a rival.
China's defending Olympic champion Chen Ruolin qualified well clear in first place ahead of Malaysia's Pandelela Rinong Pamg.