Gary Moore has set his sights on delivering his brother John a coveted milestone when the pair join forces in a new-season training venture.

Moore, who will saddle up improving colt Petronius in the Calyx@Coolmore Australia Handicap (1500m) at Randwick on Saturday, enters a training partnership with his legendary brother on August 1.

A champion trainer in Hong Kong over several decades, the 70-year-old John Moore faces mandatory retirement in the Asian racing hub this year, prompting his return home.

John Moore has long wanted to train a Group One winner in Australia and Gary is hoping they can achieve that goal together.

"He has owned one, (Queensland Derby winner) Eagle Way, but he's not going to do it by himself, he's got me to tag along," Gary Moore said.

John Moore will wrap up his Hong Kong career in mid-July before joining forces with Gary at Rosehill where they hope to expand on their current allocation of 20 boxes..

The brothers last worked together in Hong Kong in the mid-1980s when John took over the stable of their father, decorated jockey-turned trainer George Moore.

Gary says John will bring a "new edge" and fresh ideas and they have already had support from prominent owner and Everest slot holder Bon Ho, who races smart sprinter Classique Legend.

"We've got some very nice yearlings that have come into the system thanks to Mr Bon Ho," Moore said.

"He has bought some really nice yearlings out of Easter so we've got a great start."

Moore already has a nice horse on his hands in three-year-old Petronius, a last-start Warwick Farm winner who has two good runs on the board this campaign following a tie-back operation.

He says Petronius has trained on well and a good showing on Saturday could put him on a path towards the Listed Civic Stakes.

"He's got that terrific gate speed where he can take up a nice position and sustain it under heavy pressure and that's one of his attributes," Moore said.

"If we're lucky enough to win Saturday, I've got to speak to the partners, but we could consider running him in the Civic Stakes."

Randwick has been downgraded to the heavy range ahead of Saturday's nine-race card.