A filly trainer Chris Waller tried unsuccessfully to buy five months ago looms as the biggest threat to his chances of claiming Saturday's Australian Oaks.

Waller will saddle up two runners in the 2400m classic at Randwick, Adrian Knox Stakes winner Royal Descent and outsider Wind Bender.

But had fate dealt him a different hand, Waller might also have been saddling up favourite Habibi.

"We tried to buy Habibi after it won its first two starts," Waller said.

"I thought we were a bit soft with our three-year-olds but as it turns out I'm going to have two in the race anyway."

While the Oaks has long been the autumn aim for Wind Bender, Royal Descent only earned her spot last weekend when she surprised her trainer by lumping 59kg to an impressive win in the Adrian Knox Stakes (2000m), a traditional Oaks lead-up.

"I was dreading the race last Saturday because I thought it might have been a bit beyond her," Waller said.

In the immediate aftermath of the race, Waller was still in two minds about whether to press on to the Oaks.

But on reflection and in consultation with owner Gerry Harvey, he decided he had an opportunity too good to miss.

"It's a Group One race and the horse is good enough to be in the first three," Waller said.

The 2400 metres of the Oaks will be new territory for Royal Descent, as it will be for many of her rivals.

The filly won her first two starts over sprint trips and only stepped up to 1600 metres for the first time last month when runner-up to Cameo in the Keith Nolan Classic at Kembla Grange.

Waller admits her campaign since then hasn't quite gone to plan, although he isn't complaining.

"She was set for the Vinery Stud Stakes but it was too wet to run her," he said.

"Last Saturday was basically the next option without going to the paddock.

"This is her first preparation. She went to the paddock for one week but she has basically been in all the time."

A field of 11 has been declared for the Oaks including Dear Demi, who won the Victorian version in the spring, along with Vinery runner-up Longport and Victorian filly Summerbliss.