Irish jockey Jamie Spencer pulled off a classic piece of horsemanship at his first Australian ride at Flemington on Saturday.

He now needs to produce a minor miracle if he's to succeed at his second.

But the good news for supporters of the topweight and 2011 winner Dunaden is that Spencer does such things fairly routinely.

Spencer produced a masterpiece of kindness, aggression and timing to win the Mackinnon Stakes on Side Glance, after the horse had proven a handful for Craig Williams in the Cox Plate.

On Dunaden he will be required to overcome the inside gate and topweight of 58.5kg, and he's aware of the magnitude of the task.

"There's not many horses win more than one Cup because you need so much luck with 24 runners," Spencer said.

"You probably only get two or three chances in the race to make the right move.

"We're drawn in on the fence so we're going to need a bit of luck, but I'd rather that than to be drawn 24 with topweight."

Dunaden has gone largely unnoticed in training at Werribee since arriving two weeks ago, performing mostly long cantering work.

But on Sunday morning he zipped over 400m at the end of a 1600m gallop and looking a lot more like the horse who has won a Melbourne and Caulfield Cup.

"He saved the best till I got here," said trainer Mikel Delzangles who arrived in Melbourne on Saturday night.

Delzangles agreed Dunaden needed a clever ride from his barrier, to which Spencer offered a professional's reassurance.

"That's my job," he said.