The Williams family is celebrating a milestone Flemington win with former Godolphin galloper Demonstrate.

While Craig Williams and his father Allan, a former jockey and now a successful trainer, are no strangers to success at Flemington, it was the first win for Jason Williams at headquarters.

A $100,000 purchase at an Inglis Melbourne sale last December, Demonstrate followed a recent Moonee Valley win when he took out Saturday's The Melbourne Cup Carnival On Sale Handicap.

Sent off a $7.50 chance, Demonstrate scored a three-quarter length win from Concealer ($4.80) with Sunday Escape ($11) a length away third.

Jason and his father Allan prepare a team of 10 horses at Cranbourne with the majority of those for David Price in Hong Kong, however Demonstrate is one of the rare horses not in his ownership.

"It's our first win as a training partnership at Flemington and for Craig to be riding it, it's a great thrill," Jason Williams said.

"It's great to get a win at Flemington for the owners and he's almost paid his purchase price for them."

After learning Demonstrate was for sale, Williams said he wasn't leaving without him.

"I've got to thank Godolphin," Williams said.

"They tell you everything you need to know about the horse and he came to us in fantastic order.

"He might have got a bit lost in their operation and maybe that one-on-one attention has made the difference."