Rudin led home a one-two for her country, clocking 4min 39.01sec to finish ahead of compatriot Georgia Coates, with Spain’s Africa Zamorano coming through to take third.

“I had a good morning swim, but I still didn’t expect to swim so fast,” the 16-year-old from Nottingham said.

“I knew I had to go out fast to be in the mix.

“To have a one-two finish is amazing, we didn’t expect that either.”

Her triumph came after American Grant Shoults clinched the first crown of the World Junior Championships, topping the podium in the men’s 400m freestyle race.

Shoults powered to victory with a time of 3:48.91, which saw him take gold in front of Chinese duo Yang Jintong, who did enough for silver, and Qiu Ziao, who narrowly edged Australia’s Joshua Parrish by 0.01 second to secure bronze.

“I’m very happy with my time, especially because my nationals were a bit disappointing,” he said.

“It’s a great start for Team USA, as a captain I’m very excited to get the first win, this can serve as momentum for the team.

“In the race everything went perfectly, all my splits were as good as I wanted them to be and I’m pretty happy with my last hundred.”

The Australians were also in excellent form as both their men’s 4x100m freestyle and women’s 4x200m relay teams surged to gold.

Their men, comprised of Vincent Dai, Kyle Chalmers, Brayden McCarthy and Jack Cartwright, were over a second quicker than nearest challengers United States, finishing in a time of 3:17.39, while Italy took home the bronze.

Australia’s women, made up of Tamsin Cook, Lucy Elizabeth McJannett, Shayna Jack and Gemma Cooney, produced a superb display to claim the title as they clocked a world junior record time of 7:56.68.

Canada were not far behind in second, finishing in 7:57.04, while Russia rounded off the podium by sealing bronze.

The first day of the event, held at the state-of-the-art OCBC Aquatic Centre at the Singapore Sports Hub, proved to be a record-breaking one as two world junior records tumbled in the morning’s heats.

Russia’s Anton Chupkov achieved the feat by clocking 1:00.12 in the men’s 100m breaststroke, before 15-year-old Australian Minna Atherton followed suit with her time of 59.83 in the women’s 100m backstroke.