Australian 16-year-old Jacob Willcox beat 11-time world champion Kelly Slater on Wednesday at the Rip Curl Pro surf event at Supertubos in Portugal.
The wildcard from Western Australia upstaged the American world No.2 in the opening round in one to one-and-a-half metre waves.
Willcox relegated the 41-year-old Slater to the elimination second round.
"It was pretty fun out there. I got a couple of good ones," Wilcox said.
"I was stoked to get the opportunity to surf against those guys in the trials, let alone win, so I'm really happy. I got a few waves out here yesterday so I knew the banks pretty well and this is my second time competing in a WCT so I just knew I had to keep calm and it worked out pretty well."
Wilcox opened strongly against Slater, finding a big left-hand barrel to net an 8.00 point ride.
"Kelly (Slater) had priority and I was just up the beach a little bit more," Wilcox said. "This left came and I just pulled into it and got a pretty good score. That got me rolling through the heat and I managed to get a couple of other ones to back it up."
Fellow Australian Matt Wilkinson netted a 17.37 out of a possible 20 to advance over compatriot and ASP frontrunner Mick Fanning and wildcard Francisco Alves.
"I got a few okay ones at the start and it was kind of scary. I saw Mick (Fanning) get a wave before my last one and I thought it might be the score so I didn't know if I was chasing a score or not.
"That last one, I knew I was deep. I took off and was just pumping as hard as I could cause I really wanted to make it - I was stoked," Wilkinson said.
Defending event winner, Julian Wilson of Australia, scored a convincing heat win, fresh off a quarter-final berth in France and sitting sixth on the ASP rankings.
"I know I can do good here, I really enjoy these waves and I know what boards have worked here in the past. I have a lot of experience cause I've won it here before, so I take it as a positive and will take it wave by wave."
Other heat one winners included Australians Joel Parkinson, Taj Burrow, Josh Kerr and Kai Otton, along with Hawaii's John John Florence.
When competition resumes, first up will be 32-year-old Fanning against Alves in the opening heat of the elimination round two followed by Slater.
Depending on results, the second-last stop on the 10-event 2013 ASP World Championship Tour might determine the 2013 world champion.