Brazil's Italo Ferreira has won the Tahiti Pro in giant, glassy Teahupo'o tubes to showcase the wave's potential two months before the break plays host to the Olympics.

The Tokyo Games gold medallist beat Hawaiian John John Florence, who will surf for the US at the Paris Olympics, in flawless, five-metre swell.

Ferreira got the perfect start to the final, watching Florence get pummelled on his first wave then catching two absolute bombs for a pair of excellent scores.

Florence (17.16) fought back with the highest wave of the final, a 9.33 out of 10 for a fierce barrel.

But he could not reel in Ferreira, who ended with a two-wave heat total of 17.70 out of 20.

One of the first to congratulate Ferreira was jet ski-riding French Polynesia President Moetai Brotherson.

Australian Ethan Ewing was on the receiving end of a Kelly Slater buzzer-beater to lose their round-of-16 clash earlier in the day, while Ryan Callinan lost an enthralling quarter-final shootout with Brazil's Gabriel Medina, 18.96 to 15.94.

With the Olympics set to start in less than two months, the choice of Teahupo'o in the French overseas territory for the surfing competition looked inspired on Friday (AEST).

In the best surf conditions for several years on the world championship tour, almost every competitor had highlight reel moments being shot out of the giant blue barrels into cheering crowds of spectator boats in the channel.

But mistakes were punished hard.

Florence was left spitting out blood after one wipeout early in the day while Medina got clipped by the sharp coral reef at the end of an incredible cavern in his semi-final.

Ferreira, who missed out on the Brazil team for Paris such is the country's surfing depth, had earlier dispatched countryman Yago Dora in the quarter-final and then Olympics-bound Moroccan Ramzi Boukhiam in their semi-final.

Ewing (14.17) looked destined for the final eight before Slater (14.46), who had earlier scored a near-perfect 9.73, stole the win with a 4.73-point ride in the final seconds of their heat.

The 11-time world champion and five-time Tahiti title-winner scored better in his quarter-final, only to be undone by the in-form Boukhiam.

Slater, surfing Tahiti on a wildcard, is set to farewell the tour at Fiji's season-ending Cloudbreak event in late August.

Jack Robinson will join Ewing in Tahiti for the July-August Games, alongside Australia's women's contingent of Molly Picklum and Tyler Wright.

All four Australians are genuine contenders for gold in the sport's second Games appearance.

Tahitian wildcard Vahine Fierro established herself as a favourite for Olympic gold at her home break with a win over Costa Rica's world No.1 Brisa Hennessy on Thursday.

With Reuters