Having been delayed due to stormy weather north of Sydney, the tournament finally kicked off on Thursday in 1.5 to two metre waves.
And four-times world champion Gilmore of Australia did not disappoint as she earned a combined heat total of 17.75 to see off Nikki Van Dijk and Sarah Mason.
Reigning world champion Carissa Moore of Hawaii also won through after catching a last-minute wave to score 6.70. In doing so she edged out compatriot Coco Ho and France's Justine Dupont.
Another Australian to win her heat was Tyler Wright with the 2008 winner at Dee Why beating American Sage Erickson and Peru's Sofia Mulanovich.
In the opening heat of the day, Lakey Peterson beat Pauline Ado and Laura Enever.
HEAT 1: Lakey Peterson (USA) 12.75, Pauline Ado (FRA) 8.50, Laura Enever (AUS) 6.40
HEAT 2: Tyler Wright (AUS) 16.65, Sage Erickson (USA) 13.05, Sofia Mulanovich (PER) 8.70
HEAT 3: Stephanie Gilmore (AUS) 17.75, Nikki Van Dijk (AUS) 14.10, Sarah Mason (NZL) 6.80
HEAT 4: Carissa Moore (HAW) 14.05, Coco Ho (HAW) 13.50, Justine Dupont (FRA) 5.40
HEAT 5: Sally Fitzgibbons (AUS) 18.65, Malia Manuel (HAW) 15.60, Jacqueline Silva (BRA) 4.10
HEAT 6: Courtney Conlogue (USA) 14.00, Rebecca Woods (AUS) 12.35, Paige Hareb (NZL) 8.75
HEAT 1: Coco Ho (HAW) 12.05 def. Pauline Ado (FRA) 11.85
HEAT 2: Malia Manuel (HAW) 10.20 def. Sage Erickson (USA) 9.10
HEAT 3: Laura Enever (AUS) vs. Nikki Van Dijk (AUS)
HEAT 4: Paige Hareb (NZL) vs. Justine Dupont (FRA)
HEAT 5: Sofia Mulanovich (PER) vs. Jacqueline Silva (BRA)
HEAT 6: Sarah Mason (NZL) vs. Rebecca Woods (AUS)