A last-start bush maiden winner racing a long way from the national spotlight of Flemington has emerged as the plunge horse of Victoria Derby day racing.

Grafton three-year-old Blackboard Special will make his city debut at Rosehill on Saturday carrying $15 to $5 in early betting support to win the AMWU - National Handicap (1200m).

And apart from arriving in Sydney as a Grafton track record holder, Blackboard Special also brings a strong endorsement from one of racing's most experienced executives.

Michael Beattie, the Clarence River Jockey Club boss who runs racing at Grafton, says Blackboard Special is a legitimate racehorse.

"The track wasn't particularly fast when he won here the other day so I think there is plenty of merit in that (record) time," Beattie, who has almost 40 years of experience as a steward and administrator, said.

"The old saying is that times are for greyhounds and I'm a bit of a believer in that philosophy but this horse just might be the real deal."

Blackboard Special bettered previous Grafton 1100m figures held by Pentasia, a fleet-footed mare who has made her way to city company.

The time for the seven-length win on October 4 left his hobby trainer Wayne Lawson sceptical - until he watched the following race.

"It was a class one event, the barriers weren't moved and they went two seconds slower," Lawson, an electrician by trade, said.

"What surprises you is the way he does it. It just looked too easy for him and that's what good horses can do."

Lawson is taking no chances with Blackboard Special's introduction to city racing.

Horse and trainer arrived in the big smoke well before race day and the jockey who has been aboard in both starts will continue his association at Rosehill.

Matthew McGuren is entitled to claim 3kg in the city but as an apprentice heavier than most, he will ride Blackboard Special at the horse's allocated 54kg.

"The horse is not highly strung but he's got a few quirks in the barrier and the jockey knows him as well as anyone," Lawson said.