Great Britain have won men's team pursuit gold – giving Sir Bradley Wiggins a fifth Olympic gold and a British record eighth medal in all.
Britain's Ed Clancy, Steven Burke, Owain Doull and Wiggins clocked a world record of three minutes 50.570 seconds in the first round of the four-man, four-kilometres event.
Australia advanced to the final while keeping Jack Bobridge in reserve, having so far not shown their full hand.
And the perennial rivals – Australia won March's world title ahead of Britain – slugged it out for gold.
Britain were trailing until 500m to go, when a huge roar erupted from the numerous Britons in the crowd.
And Britain surged on to win gold in a world record of 3mins 50.265secs.
Australia's Alex Edmondson, Michael Hepburn, Sam Welsford and Bobridge clocked 3mins 51.008secs.
It was Britain's third straight Olympic title in the event, which Wiggins and Clancy also won at the 2008 Games in Beijing.
Bronze went to Denmark ahead of New Zealand.
Britain beat their own world record – of 3:51.659 set in winning gold at London 2012 – in the first round, effectively a semi-final, which took place 80 minutes prior to the final.
There were reports that Britain and Australia had clocked unofficial world records in training in the last 18 months and it appeared Australia had been bluffing in the first two rounds.
Australia set off faster and kept Britain at bay, but lost a rider before the 3km mark. Burke peeled off with under two laps to go, once Britain were ahead, and Wiggins took to the front. So powerful was his surge that Wiggins distanced Doull.
Three riders must cross the line to record a time and Doull clung on as Britain triumphed by 0.743.