Mitchell Larkin completed a rare backstroke double and Bronte Campbell won the blue riband women's 100 metres freestyle title as Australia celebrated another golden night at the world swimming championships.
The pair both set Oceanian records as Larkin, triumphant in the 200 metres, became the first man since Aaron Peirsol, of the United States, 10 years ago to win both the 100m and 200m backstroke at the same world championships.
For Campbell, there was the bittersweet feeling of beating her older sister Cate, who had been seeking to become the first woman to successfully defend the 100m freestyle crown but had to settle for the bronze.
The double triumph enabled the Australian team to join Britain and the US at the top of the medal table with five golds apiece with two days of the championships left.
mericans had won the last eight world 200m backstroke titles since 1998 and were counting on Olympic champion Tyler Clary or Ryan Murphy to keep the record in tact but 22-year-old Larkin again proved a class apart as he triumphed in 1 minute 53.58 seconds.
Japan's Ryosuke Irie had led for the first 100m but Larkin's powerful surge off the wall on the final turn left his rivals trailing.
Poland's Radoslaw Kawecki took silver in 1:54.55, with Russia's Evgeny Rylov taking bronze as Irie faded to fourth. Murphy could only finish fifth and Clary seventh.
"I could feel the guys next to me at my hip so I knew I was swimming well," said Larkin. "It is now a matter of lifting the levels and seeing what happens next.
"This week has been fantastic and to see the Campbell girls get first and third inspired and motivated me."
Because just minutes earlier, Campbell, only ranked world number four going into the championships, had upset the odds as she beat Sweden's Sarah Sjostrom to the wall, clocking 52.52 seconds.
Sjostrom touched in 52.70 to hold off Cate Campbell, who finished three-tenths of a second behind her sister.
"I couldn't believe turning around and seeing the time and a number one by my name," said Bronte Campbell. "It is everyone's dream and today I just happen to be the best in the world.
"I wouldn't be standing on a podium without Cate. She is my lucky talisman but every time I get on the blocks, it is every man or woman to themselves."
In a thrilling finish to the women's 200m breaststroke, the outstanding 18 year-old Japanese, Kanako Watanabe, overhauled Denmark's Rikke Pedersen to snatch gold in 2 minutes 21.15 seconds.
Micah Lawrence, of United States, came through for silver as Pedersen found herself in a remarkable three-way tie for bronze with Spain's Jessica Vall and China's Shi Jinglin.
The men's equivalent event proved equally enthralling as European champion Marco Koch improved on his 2013 world silver, the German securing gold in 2min 07.76sec.
The men's 4x200m freestyle final then provided a third dose of high-quality racing as James Guy led Great Britain from third to gold on the anchor leg as the US were beaten in the event for the first time since 2005.
Guy powered Britain's quartet home in 7min 04.33sec, with Michael Weiss fading into silver for the U.S, 0.42 seconds behind. Australia held on for bronze.
"It's the best British team we've ever had and this relay is definitely something we're going to look out for next year," said Guy, after his team had claimed their fifth gold of the championships.
