Despite trainer Robbie Laing's initial reservations about stretching So Si Bon out to a staying distance again, the talented colt will line up as a genuine contender in the $2 million Australian Derby at Randwick.

So Si Bon finished fourth in the Victoria Derby over 2500m during the spring before taking on older horses and finishing fourth over 2400m in the weight-for-age Zipping Classic at the end of his campaign.

On Saturday, the colt by dual Cox Plate winner So You Think, steps back to a mile-and-a-half on the opening day of The Championships after pressing his Derby claims with a third in the Group One Rosehill Guineas (2000m) in heavy conditions.

"We thought after the spring we might not venture right out to 2400 metres again," Laing said.

"We thought maybe a mile to 2000 metres.

"But even though he's a nuggety horse who gives the impression that he's a miler, he runs a trip."

So Si Bon is an $11 chance heading into Saturday's Classic for three-year-olds in which he will again clash with favourite Gingernuts and Inference who beat him home in the Rosehill Guineas.

With Sydney's recent wet weather, Laing brought So Si Bon home to Victoria after the Rosehill Guineas to continue his preparations for the Derby.

The Rosehill Guineas was So Si Bon's first time racing in the right-handed direction, something the two horses who beat him home had already experienced.

"So even that should improve him a bit," he said.

"It was his third run in and it's his fourth run in now and he's right at his top."

Gingernuts is the $3 favourite having won the Group One New Zealand Derby (2400m) and Group One Rosehill Guineas (2000m) at his past two starts while Randwick Guineas winner Inference is at $4.60.

Laing is hoping Gingernuts has already hit his top this campaign as So Si Bon bids to turn the tables.

"I'm only hoping Gingernuts peaked a month ago, peaked again two weeks ago and being a baby he might be on the downward spiral," Laing said.

"He was going to win by four or five lengths at the 200 the other day and right on the line, he might have eased up, but won by two.

"Inference is a very similar horse to mine. They've run third and fourth in the Victoria Derby. They've run second and third the other day with very little between them and they were both on their third run in."

Victoria Derby winner Prized Icon is also an $11 chance and will be lining up for the third week in a row.

After finishing second to Hey Doc in the Australian Guineas at Flemington on March 4, Prized Icon was unplaced in the Rosehill Guineas on March 18 but handled the heavy ground much better when second to NZ Derby third placegetter Jon Snow in last week's Tulloch Stakes.