The South Australian Derby is on the agenda for the Gai Waterhouse-trained Order Of The Sun so long as he runs to expectations in the St Leger at Flemington.

Waterhouse is chasing back-to-back wins in the Listed 2800-metre race for three-year-olds on Friday having prepared Hippopus to score a three-length victory 12 months ago.

Stable representative Mark Newnham said Order Of The Sun had a similar profile to Hippopus at the same stage of their careers.

"Hippopus ran in the Derby (in Sydney) but we decided against that with this bloke," Newham said.

"(But) they are the same type of horses."

Hippopus was second in the Tulloch Stakes and fifth in the Australian Derby before his three-length win at Flemington.

Order Of The Sun beat one runner home in the Group One Chipping Norton Stakes at weight-for-age before finishing among the tailenders after tracking a solid tempo in the Rosehill Guineas.

The colt backed up on a heavy track in the Tulloch Stakes and finished midfield, four lengths behind Darley galloper Gallatin.

"He has ran well enough up here (in Sydney) to show he's up to that grade (in the St Leger)," Newnham said.

The colt's performance is set to determine whether he heads to the Group One South Australian Derby (2500m) on Saturday week.

"If he ran up to expectations he could press on to Adelaide," Newnham said.

Order Of The Sun shares the second line of early betting at $4.40 with Throw The King, behind last start Galilee Series Final runner-up De Little Engine at $3.60.

Throw The King was fifth in the Galilee Series Final before winning over 2400m at Caulfield on Monday.

Trainer John Sadler said the gelding appeared to have come through Monday's race well and intends to back him up.

Apprentice Joseph Azzopardi claimed his first Melbourne city win on Throw The King on Monday and has kept the ride, giving him a genuine chance of a first stakes victory.

Sadler has won the St Leger twice with Full At Last in 1988 when the race was a Group Two and also 10 years later with Bohemiath as a Group Three.