A season's best performance from Britain's men's 4x400m relay team ensured the quartet qualified for Friday's Olympic final.
Jack Green put in a strong third lap before Martyn Rooney brought the Brits home in three minutes 0.38 seconds.
"I felt I had a lot to prove," said Green, who crashed out of the first round of the 400m hurdles.
South Africa, including Oscar Pistorius, failed to finish
Pistorius, the first double amputee sprinter to compete at the Olympic Games, was denied the chance to run in the semi-final as team-mate Ofentse Mogawane fell before he could pass on the baton.
But officials decided Mogawane had been blocked by Kenya's Vincent Kiilu and put the South Africans through to the final.
Britain were without world 400m hurdles champion Dai Greene, who finished fourth in Monday's Olympic final, but the quartet of Nigel Levine, Conrad Williams, Green and Rooney made strong claims to remain in the line-up for the final.
"I wanted a chance to run after my disappointment in the 400m hurdles," said Green. "I would like to think I deserve to be on this stage."
Rooney crossed the line alongside Deon Lendore, but Trinidad and Tobago were awarded first spot despite clocking the same time as the Brits.
Cuba were third, while the Bahamas, United States and Russia were the top three finishers in the second heat. Belgium and Venezuela also progressed as the two fastest losers.
Jamaica failed to qualify when Jermaine Gonzales pulled up injured in the third leg of the second heat.