Bells Beach will crown a first-time women's champion after a morning of carnage for the favourites.
Two-time defending champion Tyler Wright, fellow two-time winner Sally Fitzgibbons and world No.1 Molly Picklum were all eliminated on Wednesday in the round of 16.
Wright fell to local wildcard Ellie Harrison, who has become the giant-killer on debut in the championship tour.
A day after winning her heat and sending Picklum to the elimination round, Harrison stunned the sport again when the 18-year dispatched Wright in a tight heat.
Adding to Harrison's unlikely prominence, she will be the only Australian women's quarter-finalist.
Injury wildcard Morgan Cibilic pulled off another upset later on Wednesday in the men's round of 32 when he upset world No.4 and fellow Australian Jack Robinson.
The last heat of the day was another belter, with defending champion Ethan Ewing holding off wildcard George Pittar by the skin of his teeth.
But the surfer of the event after two days is Harrison, from nearby Barwon Heads, who has been coming to Bells Beach since she was a baby.
In a nailbiting end to their heat, Wright posted a 7.07 wave score that briefly gave her the lead.
But seconds later Harrison earned a 6.40 score that gave her the win, 13.73 to 12.79.
"As soon as I saw the heats come out, I thought 'oh no' - I look up to Tyler so much," Harrison said.
"She is the nicest person in the water, gives me compliments, she is such a cool girl.
"It's like a dream come true ... it feels a little weird, I don't know how to act."
The 18-year-old high school student is surfing in her first Championship Tour event after earning a wildcard entry.
Fellow Australian Picklum, who was the world No.1 coming into Bells Beach, also was eliminated on Wednesday morning in another boilover.
American Sawyer Lindblad beat Picklum, who had struggled in her previous two heats.
It means the two women's finalists from last year have failed to reach the last eight.
Harrison is into the quarter-finals against French surfer Johanne Defay, who beat Fitzgibbons in the opening round-of-16 heat and has replaced Picklum on top of the world rankings.
Five heats of the men's round of 32 closed out Wednesday at the Winkipop break, next to the Bells bowl.
After Cibilic dispatched Robinson, Ewing had his work cut out against Pittar.
Ewing's last wave score, a 6.43, gave him a 12.93 to 12.73 heat win.
