After passing a serious staying test with his narrow defeat in the VRC St Leger, Saint Eustace is on target for a Classic race in Adelaide.

Trained in Victoria by Mick Price and Mick Kent jr, Saint Eustace is returning to Adelaide on Saturday to contest the Group One South Australian Derby (2500m) at Morphettville.

Saint Eustace was beaten a nose by Sacramento in the VRC St Leger (2800m) at Flemington on April 25 after finishing seventh behind SA Derby favourite Dalasan in the Port Adelaide Guineas (1800m) at Morphettville on April 4.

"His run in the St Leger was a test and he came through it with flying colours," Price said.

"He was extremely unlucky not to get the photo. He was in front before and after the line, just not where it counted most.

"But importantly he was strong through the line which is a good sign for the Derby."

Price said Saint Eustace had not been pushed to handle the distance of the St Leger after having his previous start at a distance 1000m shorter.

"Whilst I had worked him for the distance, I hadn't overworked him," Price said.

"What that showed me is that he was a clean-winded staying type."

Saint Eustace will be reunited on Saturday with Zac Spain who underwent two weeks of isolation in accordance with coronavirus protocols to ride at the Adelaide carnival.

Spain scored on Oceanex for Price and Kent jr in Saturday's Port Adelaide Cup and finished second aboard Moonlight Maid in the Group One Australasian Oaks.

The jockey guided Saint Eustace to his maiden victory at Geelong over 1700m on March 14 and takes over from Michael Walker who had the mount in the St Leger.

A former Adelaide-based apprentice, Spain spent the last part of his apprenticeship with Price and rarely gets the opportunities to ride in big races.

"It's a brilliant opportunity for him," Price said.

"He's won Listed races and this is his chance now to stand up to the plate with these opportunities.

"I'm sure he'll put him in the right spot, give him his chance, and then it will be up to the horse."