The SA men's 4x400m relay team - silver medallists at the world championships last year - brought up the rear of a race where the Bahamas dramatically stole victory from the fancied Americans on the final lap.

A brilliant sprint by Ramon Miller hauled in veteran Angelo Taylor on the final stretch to give the islanders a sensational victory in a an Olympic record 2min 56.72sec.

The US took silver in 2:57.05 and Trinidad and Tobago bronze in 2:59.40.

The SA foursome of Shaun de Jager, Willem de Beer, LJ van Zyl and Oscar Pistorius, finished eighth in 3:03.46. The SA record of 2:59.21 would have been good enough for bronze.

Concerns over Pistorius running one of the three latter legs were unfounded as he took the baton without hassles - as he has done through most of his career - from Van Zyl.

South Africa won four medals at the 2011 world championships in South Korea, but so far three have not converted into Olympic silverware in London.

Van Zyl, bronze medallist in Korea, failed to qualify past the heats of the 400m hurdles, and Sunette Viljoen, also a bronze medallist, finished fourth in the women's javelin final on Thursday night.

Semenya, the 800m silver medallist last year, will take on the strongest field she has ever faced in her fledgling career at 9pm tonight.

But she should have plenty of confidence having clocked the fastest time of the semifinals on Thursday.

SA has won at least one gong in track and field at every Games since returning from isolation in 1992.

In 2008, the long-jump silver by Khotso Mokoena was the country's only medal at the Beijing Games.

In other action yesterday, Troy Prinsloo finished 12th in the men's 10km open water swim in 1hr 50min 52.9sec, less than a minute behind victor Oussama Mellouli of Tunisia, the 1500m freestyle champion four years ago.

Tiffany Kruger finished last in her heat in the women's K1 200m sprints, ending more than two seconds behind the second-last competitor.