There is a theory in racing that in-form mares are reliable betting propositions.

John Thompson is in the fortunate position of having two of them contesting separate feature races at Randwick on Saturday.

The trainer will saddle up Zanbagh in the Group Two Villiers Stakes, the major race of the Sydney summer carnival, and Jiayuguan in the Listed Christmas Cup.

A placegetter in the 2014 ATC Australian Oaks, Zanbagh has begun a career resurrection since joining Thompson's stable after her form flatlined in Victoria last season.

In two starts for her new trainer she has posted a first-up win and a fast-finishing fourth in a Festival Stakes dominated by on-pace runners.

Thompson attributes her revival to her good health.

"She came to me in very good shape, sound and happy and healthy," Thompson said.

"But I think at the end of when Guy (Walter) had her and Paddy (Payne) had her she had problems with her feet.

"But we've had no such problems at all. They're really good and, touch wood, we won't have any problems going into the future."

Thompson has experienced the problems bad feet can cause first-hand, losing stable star First Seal for the spring due to a hoof issue.

But not even a wide draw in gate 19 has quashed his confidence in Zanbagh's Villiers Stakes prospects.

"It's not ideal but we're a backmarker and the way the track played last Saturday at Randwick they were coming down the outside," he said.

A field of 20 has accepted for the Villiers Stakes, the little sister of Randwick's three feature 1600m races which include the prestigious Doncaster Mile and Epsom Handicap.

A number of the fancied runners have drawn wide including the Chris Waller-trained Telepathic in 18 and Godolphin's It's Somewhat in gate 14.

That pair is on the second and third line of betting respectively with last-start winner Happy Clapper an outright $5 favourite after drawing barrier six.

Jiayuguan will be chasing her third win in succession in the Christmas Cup and her first at stakes level.

Thompson says she is likely to be spelled after Saturday and her performance will determine which races she is targeted towards next preparation.