The United States regained Olympic track and field superiority with the last two races in the Bird's Nest Saturday, putting a week of disappointment behind them when they won the 4x400m relays.

In a night of doubles, Ethiopian Kenenisa Bekele completed the elusive 5,000m-10,000m double and Kenya cleaned up the two middle-distance races.

Combat sports again provided controversy with a Cuban taekwondo exponent banned after kicking a referee, and a British boxer claiming he was bitten by his Cuban opponent.

On the penultimate day of the Beijing Games China took an unassailable lead on the overall medal table with 49, ahead of the United States on 34, Russia with 21 and Great Britain 19.

But victories in the men's and women's 4x400m relays lifted the United States to seven athletics titles, one more than Russia and Jamaica with only the men's marathon on Sunday.

The US track team, who have suffered a week of upsets including losing their all-around sprint crown to Jamaica, recovered thanks to a remarkable run by women's anchor Sanya Richards.

The USA self-dubbed 'Dream Team' when they came to Beijing have endured a nightmare of disappointing performances including losing their sprint crown when trounced by Jamaica.

But it was the Jamaican-born American Richards who saved face when she took the baton several metres behind Russia's Anastasia Kapachinskaya and overtook her on the line.

Bekele emulated Ethiopian compatriot Tirunesh Dibaba in claiming the long-distance double - the first man to achieve the feat since another Ethiopian Miruts Yifter at the 1980 Moscow Games.

Kenya enjoyed a double gold when Wilfred Bungei won their first men's 800m title in 16 years and Nancy Langat won the women's 1500m.