The wild-card entrant defeated Hawaiian Summer Macedo in Wednesday evening’s final as event organisers managed to squeeze in a bumper day of action at Bombo Beach. 

"This is such an amazing way to end my junior career and kick off my 2018 season," Fierro said. "This is the first time I have been to the World Junior Championship and to win is so special, especially when I was so close to missing out on the event.

The men’s event was won by Hawaiian Finn McGill after he defeated Japan’s Joh Azuchi in convincing fashion. 

McGill’s victory came after after a day of upsets, with Avoca’s Callaghan one of a number of high-profile surfers to make an early exit.

After winning the women’s event last year, the 17-year-old entered the tournament as the hot favourite. 

However, she saw her title defence washed away after falling to Brazilian Taina Hinckel in the quarter-final. 

With conditions starting to deteriorate, the duo traded the lead numerous times throughout the heat. Callaghan found herself behind late in the contest and an impressive ride on a nearly unsurfable wave wasn’t enough to push her ahead. 

The loss came on a disappointing day for the Australians, with the number of Australians left in the competition going from five to zero in the space of a few hours. 

After eliminating fellow Australian Mikey McDonagh in their third round heat, Liam O’Brien was knocked out of the event after finishing third in his fourth round heat.

The loss came moments after Sandon Whittaker was bundled out of the comeptition. Whittaker held the lead early in the heat, however he was bested by eventual finalist Azuchi and Hawaiian young gun Cody Young.

Young was eliminated in the quarter-final.

The final Australian to bow out was 14-year-old Zahli Kelly.

Competing immediately after Callaghan, the Australian junior number one was defeated by Japan’s Minori Kawai.