Boom two-year-olds Rubick and Earthquake are odds-on favourites to win their respective Blue Diamond Preludes on Saturday.

Rubick and Earthquake occupy the top two lines of betting for the $1 million Blue Diamond on February 22 and make their first Victorian race appearances at Caulfield on Saturday.

The Gerald Ryan-trained Rubick opened at $2.10 with TAB fixed odds on Wednesday for Saturday's Blue Diamond Prelude for colts and geldings but quickly firmed to $1.85.

He takes on a full field in the 1100m sprint but two of his major rivals in Chivalry and Nostradamus have drawn wide in barriers 16 and 18 respectively while Rubick has gate two.

Rubick moved to Blue Diamond favouritism after a stunning debut win in slick time at Randwick on January 25.

He displaced the Peter Snowden-trained filly Earthquake as Blue Diamond favourite.

Earthquake won her only start in impressive fashion at Randwick in November and resumes in Saturday's Blue Diamond Prelude for fillies.

She opened at $2.10 on Wednesday before firming to $1.75.

Blue Diamond Preview winner Eloping is on the second line of betting in the fillies Prelude at $7.50.

Eloping's co-trainer Peter Morgan is hoping for a top three finish on Saturday to boost the future value of the filly who is already a Listed winner.

After Eloping's Blue Diamond Preview win on January 25 there was a thought the filly might head straight into the Blue Diamond without another run.

But Morgan was keen to chase more black-type with her.

"I think the Blue Diamond is going to be a really strong race this year. The Prelude is a Group Three and if we can get a place in that it's better than running fifth in the Blue Diamond," Morgan said.

"That's what we're after.

"I think she's improved since her last run. But it's not going to be easy."