The Turnbull Stakes looms as a crucial spring carnival race for Sofia Rosa who will be out to press her Caulfield Cup claims in the Group One feature at Flemington.

The Australian Oaks winner has finished 10th and ninth respectively in her two spring starts in Melbourne in the Memsie Stakes (1400m) and Makybe Diva Stakes (1600m).

Her New Zealand trainer Stephen Marsh believes a step up in distance is key for the mare in Sunday's Turnbull.

"I think she's really gone ahead since her last run," Marsh said.

"She's looking good and the step up to 2000 metres now just looks perfect.

"We would have loved a good draw but unfortunately we can't do much about that. But she goes in a lot better horse than she has in her last couple."

Sofia Rosa won the Australian Oaks (2400m) at Randwick in April and with the Caulfield Cup her target, she needs to perform well in the Turnbull where she will jump from gate 10 in the field of 13.

The mare is at $35 in Turnbull Stakes betting and $21 in the Caulfield Cup market.

"She had to get a long way back from a wide barrier last start but she hit the line well," Marsh said.

"I think the big key is the step up to 2000 metres now with a couple of runs under her belt.

"She's obviously got to put her hand and go very well on Sunday.

"We probably can't beat Hartnell. He looks the one to beat. He looks like a freak, but when we get to the Caulfield Cup we go down another three kilos.

"So we need to see a good run, hitting the line well and we can go forward to the Caulfield Cup with confidence."

Godolphin's Hartnell is the $2.10 favourite for the Turnbull after dominant weight-for-age wins in Sydney in the Chelmsford Stakes and Hill Stakes by a combined margin of almost 14 lengths.

Jameka, impressive winner of the Naturalism Stakes at Caulfield last start, is on the second line at $5.50 just ahead of The United States at $6.50.