Pounamu has caused an upset in the Kingston Town Stakes to take out the final Australian Group One race of the year at Ascot in Perth with the favourite Black Heart Bart the hard luck story of the race.

Formerly trained in NSW by Allan Denham, Pounamu now races for the Alan Mathews stable and defied his odds of $21 to win the 1800m-event.

Black Heart Bart ($3.20) suffered interference early in the race and never recovered with Pounamu swooping to beat Material Man ($31) and Acherner Star ($8.50) to make it a local trifecta.

Pounamu races in John Thompson's colours of black with a silver fern famously carried to victory in the 2000 Caulfield Cup by Diatribe.

Mathews said although Pounamu was a six-year-old, he was still a work in progress.

"He was the biggest bridesmaid in WA," Mathews told Sky Thoroughbred Central.

"All has gone to plan. We haven't had a day when everything hasn't gone right."

His jockey Pat Carbery said the win meant the world.

"Alan Mathews has always stuck solid with me for 22 years now," he said.

"I don't know if he realises how much I appreciate how solid he is. To win a Group One for him means a lot to me.

"Alan trains him (Pounamu) out of the paddock and he was in the zone today."

Pounamu had half a length on Material Man with a short head between second and third.

Black Heart Bart finished ninth of the 13 runners.