Stephanie Gilmore’s hopes of defending her World Surf League crown are hanging in the balance after becoming a victim of Molly Picklum’s giant-killing run at J-Bay in South Africa.

Picklum ousted Gilmore in the quarter-finals before edging world No.1 Carissa Moore in a thrilling semi-final to secure her spot in the J-Bay decider.

The 20-year-old, who is in her second season on the Championship Tour, will take on American Lakey Peterson in the final.

Gilmore, the eight-time world champion, pulled off an excellent 8.77 ride late in her battle against Picklum, meaning she required a 6.90 on her final wave to secure victory.

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The 35-year-old tried her best but could only manage a 5.17 on a wave that lacked power and height.

The result means world No.6 Gilmore will need to pull off a strong result in the final WSL event of the schedule – the Tahiti Pro – in order to secure a top-five berth and a spot in the end-of-season finals.

Picklum, who is now guaranteed a spot in September’s title showdown in California, followed up her win over Gilmore with a tight 10.00-9.40 victory over Moore.

Peterson ruined the chances of an all-Australian final by beating Tyler Wright in the other semi-final, 11.47 to 10.00.

Wright was lucky to make it to the final four after surviving a huge scare in her quarterfinal battle against Gabriela Bryan.

Bryan needed to score 5.34 on her final wave to overtake Wright’s two-wave tally, and the Hawaiian notched 6.27 to take the lead.

With just 10 seconds remaining, Wright set off on a wave needing 5.27 to win.

She pulled off a series of strong manoeuvres to secure a score of 5.60, handing her the win 12.93 to 12.60.

“I got my period yesterday, so today is not the greatest for me,” Wright told the WSL broadcast after scraping past Bryan.

“It’s one of those ones that before I’m paddling out I’m like, ‘I’ve got no idea how I’m going to pull it off’.

“I’m just trying to channel my period energy and just get it done so I can go back and get warm.”

-AAP