Mick Kent ran his eye over the filly Scratchy Bottom at trackwork in Adelaide on Tuesday before giving her the green light to take on the boys in the Group One South Australian Derby.

Scratchy Bottom, a fast-finishing third behind May's Dream in last Saturday's Australasian Oaks, is the only filly in Saturday's $500,000 race at Morphettville.

She has firmed from $11 to $7.50 to be on the third of Derby betting.

"I just wanted to have a look at her and see how she got through the run," Kent said.

"I came over and we gave her a canter. She looks well and has eaten up so there was no reason not to pay up."

Dom Tourneur has picked up the ride at 54.5kg and the Adelaide jockey got the chance to jump aboard the filly on Tuesday.

Kent is convinced Scratchy Bottom will relish the Derby distance.

Other options included the Queensland winter carnival or the Group Three SA Fillies Classic (2500m) on Saturday week in Adelaide.

But Kent was not keen on either of those alternatives because he wants to give Scratchy Bottom a decent spell.

"It's a Group One race and she's here (in Adelaide). The trip won't hold any fears," Kent said.

"It's hard to line them up, the colts and the fillies, but I think the fillies are comparable.

"She ran against a few of these horses in the Alister Clark Stakes and was competitive."

Scratchy Bottom has barrier one while the Gai Waterhouse-trained VRC St Leger winner and Derby favourite Order Of The Sun ($4.20) came up with barrier four.

He will be ridden by Vlad Duric who combined with Waterhouse to win last Saturday's Group One Robert Sangster Stakes at Morphettville with Driefontein.

Listed Galilee Series Final winner Bring Something ($4.80) has barrier 14 while Gamblin' Guru, winner of the Port Adelaide Guineas and Group Three Chairman's Stakes at his past two starts, will have to overcome the outside barrier.