Williams will partner the Matthew Smith-trained Buenos Noches in the $1 million Group 1 Black Caviar Lightning at Flemington.
The son of Supido was beaten a nose by Giga Kick in the Group 2 Danehill Stakes (1200m) last start, a fortnight before Giga Kick won the $15 million The Everest with Williams aboard, a race in which Nature Strip finished fourth.
Williams said that formline gives him confidence ahead of the 1000-metre weight-for-age event.
"We know this horse is very effective down the straight, Matthew is happy with the way that he's trained on and he's got within a nose of Giga Kick for goodness sake," Williams said.
"That's good enough for me, because Giga Kick is a star."
Three of Buenos Noches's five starts have been at Flemington with the Danehill Stakes run sandwiched between a Listed Poseidon Stakes (1100m) win on protest and a third placing in the Group 1 Coolmore Stud Stakes (1200m).
Buenos Noches has prepped up for the Lightning with a couple of third placings in Sydney trials with Williams getting a feel for the colt in a recent track gallop during a quick trip to Sydney.
Williams headed north to ride Queen Of Dragons for Peter and Paul Snowden in a two-year-old maiden at Canterbury on February 1, but was also called upon by Smith to partner Buenos Noches, which is what led to his Black Caviar Lightning booking.
"It was very advantageous, by chance, to get a sit on him because there was a lot that I learned in that gallop with him," Williams said.
"I was happy with his gallop, he's gallops like a good horse and there's a lot I got out of that experience."
Buenos Noches will be part of what shapes as a bumper Lightning field , headed by world champion sprinter Nature Strip. Two-time straight-track Group 1 winner Roch 'N' Horse, Golden Eagle hero I Wish I Win, star filly Coolangatta, dual Group 1 winner September Run and top Queensland sprinter Baller will also run.