Must Be Rusty zoomed straight to the front early in the 545m feature and did not give his rivals any chance of running him down in his upset victory at win odds of 28-1.
The greyhound is raced by his Darfield trainer, John McInerney, with Dunedin's Mark Thompson.
Thompson is on the committee of the Otago Greyhound Racing Club and a popular figure at Forbury Park meetings.
His involvement in greyhound ownership has spiralled after first becoming involved in a syndicate at Dunedin's St. Kilda Tavern.
''We had a pub syndicate at St Kilda, so we have been racing for about 10 years,'' Thompson said. ''But on my account I have been racing them for about three years.''
Ten years on from his first involvement, Thompson almost has too many dogs, he quipped.
''The more you've got the more chance you have got of racing a good one.''
Winning the $6245 Dunedin Cup was undoubtedly the highlight of the thrills his dogs had given him, Thompson said.
The Dunedin owner is eyeing the New Zealand Cup as a long-range target for Must Be Rusty. The chaser could not make the final of the race last year, but won a restricted-age feature on New Zealand Cup night.
''On cup night in November, last year ... he ran a faster time that the winner of the cup. He has got some class.''
John McInerney produced sprinter Wheelchair Norm to notch his 87th career victory in the race before the Dunedin Cup.