Hartnell has brought his rare Sydney spring carnival form to Melbourne, producing a breathtaking display to easily win in the Group One Turnbull Stakes at Flemington.

Giving trainer John O'Shea his first Melbourne Group One win since becoming Godolphin's head trainer in Australia, Hartnell backed up his recent big-margin wins in the Chelmsford and Hill Stakes at Randwick with a 3-1/4 length romp in Sunday's 2000m feature.

But the margin didn't do justice to the performance as Hartnell cruised away from his rivals with jockey James McDonald not raising a sweat on the gelding.

"I didn't even slap him on the neck, I just shook the reins at him," McDonald said.

"That was brilliant. It was a breathtaking performance. He's going unreal, isn't he?"

He beat Jameka by 3-1/4 lengths with the same margin back to third-placed Tally.

Hartnell is now the favourite for both the Caulfield and Melbourne Cups at $3.70 and $7 respectively and is on the second line of betting at $4 for the Cox Plate behind champion Winx who is at $1.80.

O'Shea said the decision on which race Hartnell contests next would be made by owner Sheikh Mohammed and Godolphin's John Ferguson.

"Obviously he's got plenty of options on the table and he'll be competitive in whatever he runs in. So I just hope he pulls up well and we've got a few options to consider next week," he said.

Winx beat Hartnell in the Warwick Stakes over 1400m and he has won his past three races in commanding fashion in her absence.

"You've got to be worried about the best horse in the country," O'Shea said.

"We can only look after our own house and do the best we can to prepare them the best we can and have them ready on the day. And we'll endeavour to do that whatever race we run in.

"He's got 55 kilos in a Caulfield Cup which is very inviting and the (former) Caulfield Cup favourite (Jameka) was just left in his wake there.

"But I think the program with three weeks between runs into a Cox Plate and the possibility of running in a Melbourne Cup with 55 kilos is also...I think this track suits him a little better.

McDonald said "until they clash, you don't know" in relation to a possible showdown with Winx in a Cox Plate.

"I'm happy to be on him."