Fontiton is poised the complete a rare feat in the Blue Diamond Stakes after confirming favouritism for the $1 million race with her win in the Fillies' Prelude.

The Robert Smerdon-trained two-year-old will become just the fifth horse to complete a clean sweep of their respective Blue Diamond series races if she can maintain the unbeaten start to her career in the Group One Blue Diamond (1200m) on February 28.

The only filly to have won the Preview and Prelude ahead of a Blue Diamond victory was Midnight Fever 28 years ago.

Sepoy (2011), Bel Esprit (2002) and Rancher (1982) are the colts with perfect records in the series.

Fontiton has tightened to $3 for the finale after making it three wins from as many starts in Saturday's Group Two Prelude at Caulfield, running quicker time than the colts and geldings.

Of The Brave, Pride Of Dubai and Sampeah are now considered her biggest dangers after they ran the trifecta in the male division.

Pride Of Dubai, who is expected to be a late entry for the Blue Diamond after running home hard to be beaten in a photo by Of The Brave on Saturday, is the $4 second favourite ahead of Of The Brave ($5).

Sampeah is the only other horse under double figures at $7 and will have blinkers in the big race in an endeavour to settle closer.

Smerdon has always believed Fontiton will be better as a three-year-old over longer distances and says she is doing more than he anticipated as a two-year-old.

He said her win in the Prelude, when she was under pressure coming to the turn behind a fast pace, showed she would appreciate another step up in distance in the Blue Diamond.

Jockey Mark Zahra agreed.

"The way she won it was like she was looking for 1200 metres," Zahra said.

Of The Brave kicked well clear in his division before Pride Of Dubai emerged from the pack to get close.

Both are expected to take improvement into the Diamond.

"I think there's plenty of improvement there and I think you'll find he'll be very hard to beat at the end of the month," Of The Brave's jockey Stephen Baster said.