Hartnell's devastating Hill Stakes win has rocketed him to Caulfield Cup favouritism.

And Godolphin trainer John O'Shea believes that would be his best hope of winning a spring Group One.

Jockey James McDonald had time to stroke Hartnell's mane as he cruised over the line with more than five lengths separating him from the rest of the field in Saturday's Group Two at Randwick.

He justified his $1.40 quote while Chris Waller-trained horses Who Shot Thebarman ($21) and Storm The Stars ($15) filled the placings.

Hartnell repeated his dominant Chelmsford Stakes win where he smashed a field in a race which was run without Winx after she was scratched due to the heavy track.

"Wow - he's just come back in amazing order," McDonald said.

"He's just a happy horse."

"Happy horse, happy jockey, happy trainer. It's easy isn't it?"

In Hartnell's only run last preparation he finished fifth in the Chipping Norton Stakes and was subsequently ruled out of the autumn carnival after a minor setback.

"It's unreal - he's a different horse," McDonald said.

The Metropolitan and Cox Plate remain on the table for Hartnell, whose scintillating form has made him $7 top pick for the Caulfield Cup.

"I think his best chance to win a major Group One this season would be the Caulfield Cup but Caulfield can get very firm and he doesn't like that rock-hard ground," O'Shea said.

"There is a lot of things to take into account."

Hartnell has been allotted 55kg for the Caulfield Cup.

His last two wins have been by a combined 13-1/2 lengths at Group Two level but O'Shea is keeping a lid on things.

"It was very, very good but I don't know if he had too much to do," O'Shea said.

"Maybe the opposition was a little bit flat."

O'Shea said he wanted to keep Hartnell in Sydney as long as he could to utilise Godolphin's Osborne Park training facility.

But there is little doubt the horse is Melbourne-bound as he tries to add a second Group One to his win in last year's BMW.