In-form Australian surfer Joel Parkinson posted the highest heat score of the year to throw down the challenge to runaway WCT series leader Kelly Slater at the Billabong Pro Mundaka in Spain.

He had a two-wave score of 19.70 points out of a possible 20.

Gold Coast-based Parkinson, 25, showed he meant business against compatriot Jarrad Howse from the outset - nailing 9.97 on his first wave.

Far from satisfied, Parkinson continued to chop up the one to two metre swell to follow with a 9.73 effort and capped the amazing performance with an equally impressive 9.40 on his final wave.

Parkinson stayed true to his pact with fellow Gold Coaster Mick Fanning to "do anything we can" to stop Slater who can claim an eighth world title with victory at Mundaka.

Fanning also kept up his end of the bargain with an impressive third-round win over fellow Aussie Toby Martin, notching a 9.17 ride.

Their efforts were noted by Slater who spent the day as a spectator, the tide-sensitive river mouth stopping wave production just before he was due to take to the water.

Parkinson and Fanning are due to meet in the quarter-finals if they keep winning.

Slater (7017pts) leads the series ahead of Taj Burrow (5968), Andy Irons (5841), Parkinson (5584) and Fanning (5341).

Tom Whitaker also won through to the fourth round but other Australians eliminated were Darren O'Rafferty and Nathan Hedge in the second round and Luke Stedman in the third round.

Slater will take on local hope Hodei Collazo when third round action resumes.

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