Five-time world surfing champion Stephanie Gilmore will have to fight to stay afloat at the women's world tour event in California after she missed out on direct entry into the quarter-finals.

Gilmore scored a two-wave combined score of 10.00 points in the third round of the 2013 Vans US Open on Thursday, but was bested by local contender Courtney Conlogue, who scored 15.43 in front of her home crowd.

The defending world champion will now have to compete in Friday's fourth round to stay in contention.

Two other Australian contenders, Tyler Wright and Sally Fitzgibbons, topped their heats and coasted straight through to the quarters.

Wright posted 15.67 in the second heat, ahead of Bianca Buitendag (11.00) and compatriot Laura Enever (6.33).

Wright, 19, who is currently leading in the ASP tour rankings, said luck was a factor in her round-topping score.

"I couldn't catch a wave out there, but the tide was super high and I was expecting it to be slow," she said.

"I was lucky to get that first one."

Wright shared pole position with Hawaii's Coco Ho, who also scored 15.67 in her heat.

Meanwhile, Fitzgibbons' 14.33 effort edged out France's Pauline Ado (14.20) to win her a place in the quarter-finals.