RIDING HIGH: Billy Stairmand's boilover win at the Telstra Drug Aware Pro event is reflected in his new world ranking.

Raglan surfer Billy Stairmand has beaten 10 times world champion Kelly Slater in a massive boilover at the ASP Tour event in Western Australia.

The young Kiwi held his nerve to overhaul Slater and then hang on for a 16.50 to 15.50 win - arguably the biggest result in New Zealand surfing history.

It was achieved in powerful three to four metre waves at the famous Margaret River break south of Perth and put Stairmand into the final 12 of the Telstra Drug Aware Pro.

Slater set the early pace with a 7.50 in the US$285,000 event. Stairmand equalled that soon after and then scored an incredible 9.00 with five minutes of their man on man heat remaining.

That left Slater needing to better a 9.00 to snatch victory.

The American used all his experience to throw everything at Stairmand, scoring a 6.93 and an 8.00 in a late flurry that came up just short.

Stairmand ran out of steam later in the day. He finished second in his round of 12 heat forcing him into a repechage heat against Brazil's Dream Tour competitor Jadson Andre. In deteriorating surf Andre won 12.10 to 10.60 to go into the quarter-finals.

Stairmand exited with $US5000 but the prize scalp of Slater fresh in his memory.

Slater made the unusual decision to contest this secondary tour event because of the fantastic conditions and he wanted practice ahead of the looming Rip Curl Pro, a Dream Tour event at Bells Beach in Victoria.

The 21-year-old Stairmand is no stranger to success having won a six-star event on the secondary tour in Spain late last year that signalled his potential.

But this is a completely different level.

Stairmand is ranked No 58 in the world and Slater is No 1 and acknowledged as the greatest competitive surfer of all time.

Richard Christie, New Zealand's other surfer in the final 24 of the Western Australian event, went close to pulling off a major upset himself. Up against Mick Fanning, Australia's double world champion, the Mahia youngster eventually bowed out 13.70 to 10.00.

Taranaki's Paige Hareb is through to the quarter-finals of the women's event which are likely to be surfed tomorrow.