Britain's Tom Daley and Pete Waterfield missed out on an Olympic medal in the synchronised 10m platform event after coming fourth at the Aquatics Centre.
Daley, 18, and his 31-year-old team-mate had led the competition after three of their six dives but a poor next effort saw them drop to fourth.
One mistake can prove costly and, unfortunately, that is what happened to our boys. The all-important fourth-round dive is, ironically, their best dive. In training, they have been exceptional. But Tom came out too early and Pete too late. Both made a different error. As soon as you hit the water, you know. There is no magic rewind button. When it mattered, they faltered - and what a shame it was.
China's Yuan Cao and Yanquan Zhang took gold with a total score of 486.78.
Mexico clinched silver on 468.90 ahead of the United States duo on 463.47 with the British pair on 454.65.
It was an anti-climactic end to a competition that promised so much, the deafening home support ebbing away with the hopes of Daley and Waterfield.
In the first two compulsory rounds, the Britons had been exceptional, going past the Chinese favourites with a score of 56.4 from an inward dive to lead by 0.60 points.
They extended that lead in the third round when their back three-and-a-half somersault was given a score of 91.08. That meant, with three dives left, they led Cao and Zhang by 2.4 points with Germany's Patrick Hausding and Sascha Klein in bronze.
But the Chinese, just 17 and 18 years old and winners of the World Series events in Beijing and Moscow earlier this year in addition to the test event here in February, increased the pressure with 93.06 points for a reverse three-and-a-half somersault.
That is when the British pair cracked. Going for the same dive, Waterfield over-rotated and his entry was poor. The judges awarded a score of just 71.28 - and in that instant the gold medal was gone.
Fourth place 'agonising' for Daley
The Chinese had a 19-point advantage over the home favourites and increased the gap between them and the pursuing pack with a 92.66 off a back three-and-a-half somersault in the penultimate round.
Daley and Waterfield still had realistic hopes of a medal, but Daley was fractionally off on their extremely testing forward four-and-a-half somersault.
When their final dive - a back two-and-a half somersault with two-and-a half twists - scored them no more than 91.80 for a total of 454.65, their fourth place was confirmed.
Mexican pair Ivan Garcia Navarro and German Sanchez Sanchez snatched silver with an audacious final dive to leave the USA's Nicholas McCrory and David Boudia with the bronze medal.
If the margins seemed fine, that is the nature of the sport. Daley, one of the best-known British athletes competing in London, will now pin his medal hopes on the solo 10m platform competition on Friday, 10 August.