A Group One start for promising filly Heatherly will be determined by her performance in a sprint race at Caulfield.

Prepared by training partner cousins Mathew Ellerton and Simon Zahra, Heatherly will contest the Rubiton Stakes over 1100m on Saturday.

Success will have the filly heading to the Group One Oakleigh Plate over the same course and distance on February 27.

"She needs to win it on Saturday and gain a penalty to get into the Oakleigh Plate," Zahra said.

"We'll just get past this first and then see what happens."

Heatherly is aiming for her third win in succession after victories at Moonee Valley and Flemington.

Her latest came in three-year-old fillies grade over 1100m where she carried 56kg and on Saturday drops to 51kg.

Zahra said the wins had brought further improvement in Heatherly and that has translated into some impressive workouts on the track.

"She's been relaxing and hitting the line," Zahra said.

"She used to be so fierce in her work.

"She would be gasping for air but now she is relaxing and picking up nicely and is putting it together.

"I'm really happy with her condition. She's looking the best she ever has but she has to going into a race like that on Saturday."

Heatherly opened favourite for the Rubiton at $3.80 and has firmed into $3.60.

Politeness, from the Robert Smerdon stable, is back after a spell and is looking to build on her first-up record of three wins from seven starts.

She is now vying for favouritism with Heatherly after firming from $4.20 into $3.80.