Riff Rocket has raced to a rare staying double and in the process delivered Sydney's premier trainer Chris Waller with his first ATC Australian Derby success at Randwick.

Waller admitted it had been a source of a little frustration that he had yet to train the winner of the time-honoured Australian Derby during his remarkable career, but he no longer needs to worry about that after Riff Rocket raced to a memorable victory on Saturday.

In adding the Group 1 ATC Australian Derby to his record, Riff Rocket became just the fourth horse to claim both the Victoria Derby (2500m) in Melbourne in spring and the Australian Derby (2400m) in Sydney in autumn.

Hitotsu achieved the feat two seasons ago with Mahogany (1993-94) and Dulcify (1978-79) the others to win the double.

Riff Rocket has also won the Group 1 Rosehill Guineas (2000m) this autumn, beating the Joe Pride-trained Ceolwulf, and it was that pair who again fought out Saturday's Derby.

James McDonald was able to steer Riff Rocket through the pack from back in the field at the right time and the $2.20 favourite defeated Ceolwulf by a neck with another 4-1/4-lengths back to Glad You Think So in third.

"It's pretty special," Waller said of his first ATC Australian Derby win, which took the trainer's Group 1 tally to 160.

"I didn't think the media had caught up that we hadn't won it yet.

"It was bugging me a little bit that we hadn't won it. We haven't had that many chances, I don't think.

"So it's a good one to win. It's an important one to win. We train a lot of stayers and to get the horse to win a Rosehill Guineas and be favourite and get here (and win), it's a pretty big deal."

Connections made the decision to chase the Derby double with Riff Rocket after the three-year-old won the Rosehill Guineas two weeks ago and the decision to stretch him back out to a Derby distance was rewarded.

"We did it properly, we assessed after the Rosehill Guineas where he fits in and the form experts said go to the Derby," Waller said.

"Simple as that.

"He's done a great job, he's an amazing horse. He puts himself into the race at the right time."

McDonald is adamant the Derby distance is not Riff Rocket's best distance but he praised the gelding's will to win.

"I was (concerned) at the 300 (metre mark), because he didn't spend a penny getting there but I could feel he was out on his feet because the distance range is as far as he wants," McDonald said.

"But his will to win, tenacity and finding the line is incredible."

Blake Shinn said Ceolwulf was brave in defeat and predicts a bright future for the colt.

"The winner got the breaks up the middle," Shinn said.

"We had to come wide. Great race. He could turn the tables down the track. He's an exciting talent."