Olympics:Jamaica's bid for the men's 4x400 metre relay gold was cut short by injury when Jermaine Gonzales pulled up in qualifying, while South Africa went through on appeal after their race ended in a collision with Kenya.
World championship bronze medallists Jamaica had fancied their chances of ending America's dominance in the event, and looked devastated when Gonzales, who has struggled recently with a hamstring problem, stopped and sank to his knees in the third leg of the second heat.
Usain Bolt, the world's fastest man, had said there was a slim chance he might have run in the final for Jamaica. "I feel sorry for him. I am not going to put him down or anything, he tried. I am still proud of him," team mate Errol Nolan said of Gonzales.
On a day of drama inside a boiling hot Olympic stadium, there was also initial despair for South Africa and their double-amputee runner Oscar Pistorius, whose much anticipated relay run never materialised.
Pistorius, who races wearing carbon fibre prosthetic blades after being born without a fibula in both legs, had to watch in disbelief as his compatriot Ofentse Mogawane collided with Kenya's Vincent Mumo Kiilu on the last bend of the second leg and was too hurt to continue.
As Mogawane came around the last bend it appeared that Kiilu cut across him and caused the collision, sending both runners flying. Mogawane was left in a heap clutching his left shoulder and Kenya were later disqualified for the incident.
After an appeal the IAAF placed South Africa in the final.