Irish horse Hunting Horn has firmed for the Melbourne Cup after winning the Moonee Valley Gold Cup in his first spring carnival appearance in Victoria.

From the stable of champion Irish trainer Aidan O'Brien and ridden by Ryan Moore, Hunting Horn was well supported to start $4.20 in Saturday's Group Two Moonee Valley Gold Cup (2500m) and drew away from Mr Quickie over the final 150m to score by 1-1/4-lengths.

Downdraft, trained by O'Brien's son Joseph, was a neck away third.

After the win, five-year-old Hunting Horn firmed from $51 to $18 for the Melbourne Cup (3200m) on November 5.

Hunting Horn was already in the Cup field at 20th with 55kg and is eligible for a weight penalty for Saturday's victory.

O'Brien's travelling foreman T J Comerford said.Comerford said Hunting Horn was straightforward and should not have a problem with Flemington.

"You don't know until the day. It's a big step up in trip as well," he said.

"You have a lot of things going against you. A mile and a quarter (2000m) is probably his ideal trip but at the same time you don't know until you step them up how their stamina kicks in.

"Aidan is quietly confident that there's another good day in him. But he won today anyway and that's the main thing.

"It was a class ride by Ryan Moore."

The victory was the well-travelled Hunting Horn's third win from 22 starts.

"He's a lovely colt," Moore said.

"He's had very good form all the way through. He's had some tough assignments. He's a Camelot and they have a little bit of brilliance."

Trainer Phillip Stokes ruled out going to the Melbourne Cup with Mr Quickie, who was second emergency for Saturday's Cox Plate (2040m) and instead ran over 2500m when he did not get a start in the feature.

"He presented to win and didn't run it out," Stokes said.

"I've always had that query. We're not pushing on to the Cup."

Humidor was another Cox Plate emergency who ran in the Moonee Valley Gold Cup, finishing fourth.