Landing the ATC Australian Derby ride on Puccini has come as a welcome surprise for jockey Craig Williams.

Michael Walker rode Puccini to win the New Zealand Derby but he lost the mount after the three-year-old struggled in the Rosehill Guineas.

Puccini's trainer Peter McKay told New Zealand media the horse's connections dumped Walker for not taking a trail while the Cox Plate winner Shamus Award raced keenly in the early stages of the Guineas.

Ironically, Williams was aboard Shamus Award.

Williams said he only found out he had the Derby ride on Puccini when he finished riding work at Warwick Farm on Tuesday morning.

"I don't know what transpired but he's a good ride to have in the Derby," Williams said.

The jockey said his pre-Rosehill Guineas study of Puccini left him confident the kiwi could bounce back from his last-start disappointment.

He rates Puccini as one of the three top chances for the Derby.

"I did my video tapes of Puccini before we competed against him and I saw he is a high-quality staying three-year-old," Williams said.

"I'd say the number one and two choices in the race would be Criterion and Thunder Fantasy."

Criterion and Thunder Fantasy finished together when fourth and third respectively in the Victoria Derby in the spring while they ran first and second in the Rosehill Guineas.

Bookmakers agree with Williams's Derby assessment.

They have Criterion as $3.50 favourite while Puccini and Thunder Fantasy are next at $8.