Kelly Slater opened the door a fraction for the Australian pretenders to his world surfing crown with a shock third round defeat at Teahupo'o in Tahiti.

Defending the Teahupo'o title he's won more times than anyone else, 11-times world champion Slater was toppled by hot Brazilian wildcard Ricardo Dos Santos on Sunday (Monday AEST).

The 40-year-old American was undone as Dos Santos outpointed him in dramatic fashion with a two-wave combined heat total of 18.34 points to 16.44.

Needing a major score with just 10 seconds remaining in the heat, Dos Santos threaded a lengthy forehand barrel to score 9.87 out of a possible 10 and snatch an emotional win.

"I honestly don't know a whole lot about Ricardo," Slater admitted.

"I know that he won the (qualifying) trials here last year in huge surf and won the trials this year in small surf so he's obviously very competent out here in any kind of conditions."

It means Slater is credited with an equal 13th place result - his worst on the world tour since May last year when he bombed out in Rio de Janeiro.

Slater, who won the previous event in Fiji, is sitting second in the 2012 world championship near the midway point behind Australia's Mick Fanning, who won at Bells Beach, while Fanning's countrymen Joel Parkinson and Taj Burrow are third and fifth respectively.

Two-time world champion Fanning and Parkinson both went on to win fourth round heats later in the day to reach the quarter-finals while Burrow faced a fifth round elimination heat after coming second to Fanning.