Melanie Schlanger anchored the Australians to Olympic gold in the women's 4x100 metre medley Saturday.
Schlanger, who was on the 4x200m gold-winning team in Beijing, held off a late charge from Ranomi Kromowidjojo to take first place ahead of the Netherlands.
The US had led after strong legs from Missy Franklin, Jessica Hardy and Lia Neal, but Schlanger timed her final burst to perfection, securing the win by more than half a second.
Kromowidjojo swam the race's fastest 100 meters with 51.93, which sealed the silver for a Netherlands team that had not been in the top three until the final leg.
The US ended with a second off the pace to take the bronze, while China, a persistent threat throughout, was bumped off the podium at the last.