World No.3 Stephanie Gilmore was ousted in the elimination round by fellow Aussie Isabella Nicholls at the World Surf League event in Brazil.

Stephanie Gilmore's bid for an eighth world surfing title has suffered a blow as she was beaten by fellow Australian Isabella Nicholls at the WSL event in Rio de Janeiro.

Ranked third going into the eighth championship event, Gilmore (1070) fell to seventh-ranked Nicholls (11.16) in the elimination round in clean three-to-four foot surf at Saquarema on Friday.

"It's a bummer to come to Brazil and have an event go like that," said Gilmore.

"It was just the conditions, I felt like I could get the scores if I could just get the waves, but I couldn't.

"Isabella (Nichols) was in the perfect place for that right hander and that was really the best wave of the heat, that's just how the cookie crumbles."

Nicholls joined fellow Aussie Sally Fitzgibbons in the quarter-finals, but both failed to progress any further.

Brazil's Tatiana Weston-Webb beat Nicholls to set up a semi-final against five-time world champion Carissa Moore, who defeated wildcard Caroline Marks.

France's Johanne Defay ousted former Brazil winner Fitgibbons and will meet Gabriela Bryan in the semis after Bryan beat Lakey Peterson.

The men's elimination round was also contested with Australians Ethan Ewing and Callum Robson advancing to join fellow Aussies Jack Robinson and Connor O'Leary in the round of 16.