Rillito comfortably justified odds-on when winning her maiden over 1150m on the inner track at Newcastle on November 7 at her second start and first this preparation.
On
"It's a big challenge Saturday, but she is a filly we have got a good opinion of,” O'Shea said.
"She went to the Valley on Tuesday for a look and pleased with a good piece of work with an older horse.”
Rillito galloped with Sarajevo over 1000m, accelerating home the last 600m in 37.46 seconds, the last 400m in 24.16 and finishing together.
One of five last start winners in the race, Rillito has the advantage of carrying 55kg, the lightest weight in the race where Gold Busker is the 60kg topweight.
"It's hard to get a line on what she beat and what she gained in terms of experience from the win at Newcastle," O'Shea said.
"Her trials had been really good going into it and she went and got the job done nicely.
"She's a progressive filly, we'll find out how much on Saturday.”
Rillito is available at $4.20 with Sportsbet behind $3.90 favourite Divine Mr Artie.