Haybah has not figured in Lindsay Park's Blue Diamond Stakes plans and trainer David Hayes admits it is because the filly has been a surprise packet.

The last-start stakes placegetter gets her chance to snare a Group Three win in the Chairman's Stakes on Saturday at Sandown against a field which includes Maribyrnong Plate winner Prompt Return and Merson Cooper Stakes winner Thurlow.

Hayes will also run first-starter More Than Most which unlike Haybah, does hold a Blue Diamond nomination.

An on-speed filly, Haybah broke her maiden at her fourth start and it took Blue Diamond favourite Fontiton to run her down last start in the fillies' Preview at Sandown.

"She's crept up on me a bit," Hayes said of Haybah.

"I thought she was a bit off the good ones. Then she stretched the favourite a bit last start."

Haybah is on the second line of betting at $4.20 but Hayes concedes he fears top fancy Prompt Return.

The Danny O'Brien-trained colt is also prominent in Blue Diamond betting and O'Brien has declared Prompt Return ready to rumble first-up.

"We're not going there half-hearted on Saturday," O'Brien said.

"He's there to win. He's a colt and he's done enough to be winning. There won't be any excuses."

Prompt Return has eased slightly but remains top pick with bookmakers at $3 while More Than Most, who opened at $10, has tightened to $7.50 for the Chairman's Stakes.

Hayes said the unraced youngster had shown ability in his two barrier trials.

"He's probably more a 1200 to 1400-metre horse but the stable has a nice opinion of him," Hayes said.

Stablemate Keen Array, a Bel Esprit colt, makes his debut in Saturday's Inglis Premier (1000m) and has also been a notable firmer in early markets.

"He has trialled well in private," Hayes said.

"He's a fast horse and should sit on the pace and be pretty competitive."