Cascadian has left it until the last minute to guarantee himself a berth in the Doncaster Mile with victory in the Prelude at Rosehill.

The carnival is scheduled to move to Randwick next Saturday when the $3 million Doncaster is one of the features on the first day of The Championships.

Trained by James Cummings for Godolphin, Cascadian ran fifth in the Liverpool City Cup three starts ago, losing all chance when he was involved in a scrimmage which resulted in a suspension for his jockey Glen Boss.

He was in a spot of bother again in the Ajax Stakes when he ran third but did everything right on Saturday in the Group Three Prelude (1500m), beating Mask Of Time and Gaulois.

Cummings said he would wait to see how he came through the win before committing him to the Doncaster.

"He has been blocked, blocked, blocked, all campaign and then he does that seven days out from the Doncaster," Cummings said.

"It was exciting.

"We pegged him as a Doncaster horse since he ran third in the Cantala in the spring and it took until now for him to get there.

"There is no guarantee we will run him but he is absolutely flying.

"I had a really good feeling he was coming to a peak this preparation. He was ready to run a big race."

Cascadian's win was the fourth on the day for James McDonald who copped the brunt of the Liverpool City Cup interference on Imaging.

"He gave me a really good feel. That gets him exempt into the Doncaster and who is to say that he can't be right in it right up to his ears," McDonald said.

"He burst through. He was held up for a long way up that straight. He got out with a furlong to go and he was great. He wanted to have a good crack.

"It was a great day for sure ."

McDonald's wins included the Group One Tancred Stakes on Verry Elleegant but he had to settle for fourth on odds-on favourite Funstar in the Vinery Stud Stakes won by the Gai Waterhouse and Adrian Bott-trained Shout The Bar.

The past two Saturday carnival meetings at Rosehill have been held amid strict biosecurity protocols with officials hoping racing can stay up and running for the rich Championships.