An administration mistake has landed Grand Marshal a Moonee Valley Cup.

The Chris Waller stable had Grand Marshal geared towards last Wednesday's Geelong Cup but inadvertently accepted with Who Shot Thebarman in the 2400m race.

Once the mistake was discovered, Who Shot Thebarman was immediately scratched with the pair lining up in Saturday's 2500m Moonee Valley Cup.

Ridden by Ben Melham, Grand Marshal ($19) scored a three-quarter length win from his stablemate, the $4.40 favourite Who Shot Thebarman with Pentathlon ($61) 3-1/2 lengths away third.

Waller said both stayers are now bound for the Melbourne Cup at Flemington on November 1.

In a change of routine for the stayers, Waller elected to run the pair in the Moonee Valley Cup instead of the more tradition path of the Caulfield Cup.

"I remember sitting up in the stand last year and thought it was a good race and sure enough the form was franked in the Melbourne Cup," Waller said.

"It's another big step in 10 days but they'll go into the race in good form."

Melham has put his hand up for the ride on Grand Marshal in the Melbourne Cup and said any rain would enhance his chances.

"He hit his right surface today being able to get his toe into the track," Melham said.

"He's a two-miler and any rain would help him.

"He appreciates a bit of a quieter ride and the race set up well for him as there was a solid pace throughout.

"Hopefully he's got a bit of confidence from that win today."

Bookmakers reacted to the victory with Grand Marshal firming from $51 to $17 while Who Shot Thebarman shortened from $26 to $21.

Racing Victoria handicapper Greg Carpenter will announce any Melbourne Cup penalty on Monday.