Fontein Ruby faces a distance test in the Caulfield Classic on her way to a potential Oaks start.

The Robert Smerdon-trained filly scored a determined on-speed win in the Edward Manifold Stakes over 1600m last start to bring the VRC Oaks into focus.

She steps to 2000m in Saturday's race where her opposition includes colts and geldings as well as her stablemate Crafty, the filly who flashed home for third in the Edward Manifold.

Smerdon said it was unknown whether Fontein Ruby, a daughter of Turffontein from unraced Rubiton mare Charming Ruby, would be strong at the trip but he also said she deserved her chance.

"What you do in trackwork is all speculation. You never gallop them at race tempo over that sort of distance. You've only really got to put them to the test and give them the opportunity," Smerdon said.

He admitted her breeding suggested the distance might be beyond her but noted horses can defy their breeding, especially against their own age.

"You've got to believe what you see," he said.

"She was so tough at the end of a mile and it's very hard to lead over a mile.

"Out to a bit steadier tempo, we'll give her her chance."

Crafty was originally going to run in the Ethereal Stakes (2000m) for fillies but will also take her place against the males.

Smerdon said Crafty looked like she would relish the distance of Saturday's race.

The Caulfield Classic, formerly Norman Robinson Stakes, has had a significant prize money injection to $750,000.

Crafty is on the second line of VRC Oaks betting at $7 behind stablemate Lumosty ($6) with Fontein Ruby at $10.

Caulfield Guineas fourth placegetter Kumaon is the $4 favourite for the Caulfield Classic ahead of Merion who ran wide around the turn in the Guineas last Saturday before finishing sixth.

Bachman and Magicool are both at $6 with Crafty at $7 and Fontein Ruby $9.