US rider Kristin Armstrong takes time-trial gold as Team GB's Emma Pooley finishes sixth

(AP)

The United States' Kristin Armstrong successfully defended her Olympic time-trial title at Hampton Court.

Armstrong finished the 29-kilometre route in 37 minutes 34 seconds to finish 15 seconds clear of the field.

World champion Judith Arndt of Germany finished in 37mins 50secs to place second, with Russia's Olga Zabelinskaya third in 37:57 for her second bronze medal of the Games.

Great Britain's Emma Pooley, the 2010 world champion and silver medallist in Beijing four years' ago, finished in 38:37, placing sixth.

Lizzie Armitstead, Britain's first medallist of London 2012 after winning silver in Sunday's road race, clocked 39:26 to place 10th.

Armstrong was the last of the 24 riders to roll down the ramp and was quickest at the first time-check, after 9.1km, clocking 13:56.

Linda Villumsen was one second behind and Pooley was fourth quickest in 14:06.

Armstrong was four seconds faster than Villumsen at the second time check, with 8.6km remaining, in 27:13, while Pooley was sixth 32 seconds behind.

The flat nature of the course did not suit Pooley and she finished well behind as a dominant Armstrong triumphed.

PA