(Adds details) By Martyn Herman RIO DE JANEIRO, Aug 13 (Reuters) - The battle on the boards between Britain and the United States for Olympic women's team pursuit gold sizzled on Saturday as the two favourites traded world records in quick succession. Sarah Hammer's American outfit threw down the gauntlet with a superb ride in their heat against Australia, clocking four minutes 12.282 seconds for the 4,000m endurance event -- a second quicker than Britain's time in Thursday's qualifiers which itself was a world record. The brand new Olympic velodrome has already witnessed six world record rides, including two by the British team pursuit squad led by Bradley Wiggins who beat Australia to gold in an epic duel on Friday. More...