Winona Costin has designs on one day riding at Australia's biggest racing carnival but for now her focus is on the tough task of defending her Sydney apprentices' title.

The young rider has a great opportunity to add to her season tally of winners at Rosehill on Saturday with a full book of nine mounts.

With most of Sydney's best senior riders competing at Flemington during the Melbourne Cup carnival, opportunities for the better junior riders swell and Costin is determined to make the most of them.

Last season's champion Sydney apprentice, Costin is due to come out of her time next autumn and knows winning back-to-back titles will be a challenge.

"It would be awesome to do that, but obviously it will be a lot harder," Costin said.

"Last year I started the season with about 18 winners before I outrode my three kilo claim, this season I've got one-and-a-half kilos and I'm on my way to losing my whole claim so it will be a lot harder this year."

Sam Clipperton won the junior riders' crown a year before Costin and he will be part of Derby day at Flemington where his rides include Man Of Choice in the blue riband and Stay With Me in the Myer Classic.

Costin hopes she can be part of the Melbourne spring carnival at the corresponding time next year.

"I missed out on Melbourne Cup day this year but hopefully next year I can get down there and at least ride in one race," she said.

Some of Sydney's biggest stables have called on Costin for rides at Rosehill including Chris Waller.

But arguably Costin's most important ride will be on We're Sure for her bosses, Peter and Paul Snowden.

The three-year-old resumes following an initial campaign that yielded a provincial win and a fifth to Victoria Derby contender Shards.

"He has filled out a lot more now, he's a big strong horse," Costin said.

"He has been trialling really well and his trackwork has been great."