Rio de Janeiro: Australia's champion women's 4x100 metres freestyle quartet have announced themselves as the country's greatest relay team with the second gold medal of a thrilling first night at the Olympic Aquatic Centre.

Already Mack Horton had opened Australia's account in Brazil in the 400m freestyle final and Cate Campbell, Bronte Campbell, Emma McKeon and Brittany Elmslie completed a double by defending the relay team's title from London four years ago.

A brilliant third leg from Bronte Campbell booted the Australians to the front before her sister put on the finishing touches to lead Australia home in a world record time of 3.30.65. The United States, anchored by a gutsy Katie Ledecky, were second in 3.31.89 with Canada claiming the bronze in 3.32.89.

McKeon began strongly for Australia, handing over to Elmslie only 0.05 seconds behind the Americans, but the US were booted in front by nearly half a second at the halfback mark thanks to Dana Vollmer.