Australian Molly Picklum has joined world No.1 surfer Gabriela Bryan as the only top-five women to avoid the elimination round at the Trestles Pro.

Jack Robinson also won his round-one heat, while fellow Australians Joel Vaughan and Ethan Ewing have stayed alive on the opening day of the World Surf League round in California.

But event wildcard Kelly Slater, the 11-time world champion, is out after losing his elimination heat.

Picklum is ranked third in the world after seven events and she is through to the round of 16 after taking out her opening heat.

But compatriot Isabella Nichols, the world No.4, American defending world champion and second seed Caitlin Simmers and Hawaiian Bettylou Sakura Johnson, ranked five, all must battle through the elimination round to stay alive at Trestles.

Australian two-time world champion and world No.6 Tyler Wright is another big name forced into the four elimination heats.

Only American Lakey Petersen had a higher opening heat score than Bryan, the in-form Hawaiian who won the previous round at Margaret River.

In the men's draw, Robinson was the only Australian to take out his heat, while South African world No.1 Jordy Smith also won.

Vaughan was second behind American Griffin Colapinto and Ewing was third in the heat, meaning the two Australians went into the elimination round.

The Australians then beat their Brazilian opponents, with Vaughan eliminating Miguel Pupo and Ewing downing Alejo Muniz to stay alive.

Competing on the world tour for the second time this year, 53-year-old Slater finished last in his opening-round heat.

The American had a tight elimination-round duel with Hawaiian Barron Mamiya before the world No.5 knocked out Slater, posting the best wave score of their heat with less than three minutes left.