Australia's Olympic silver medallist Jack Robinson has locked in a spot in the title-deciding World Surf League (WSL) Finals after winning a tense round-of-16 clash in the Fiji Pro.

Ranked number three in the world heading into the final stop of the regular season, Robinson only needed the victory on Friday to secure his berth in the WSL Finals at Lower Trestles in California next month.

The Finals feature the top five on the men's and women's rankings in a one-day, winner-take-all showdown.

Robinson had to scrap his way to a win over Australia-born Connor O'Leary, who now competes under the Japanese flag.

Robinson trailed O'Leary until the final few minutes at Cloudbreak when his rival blew a golden chance to extend his lead, falling on one of the waves of the heat.

The West Australian then took his own opportunity, scoring a 5.67 for a combined total of 12.34 to topple O'Leary's total of 11.50.

Robinson will face in-form Brazilian Yago Dora in the quarterfinals.

Queenslander Ethan Ewing was ranked world number five heading into Fiji and will take on fellow Newcastle veteran Ryan Callinan later on Friday to keep alive his hopes of a place in the Finals.

The women's field completed their elimination round early Friday, but Australia's world number four Molly Picklum and 10th-ranked Tyler Wright had already moved safely through after heat victories.

AAP