Onesmoothoperator has announced himself as a contender for Australia's most famous horse race after claiming the Geelong Cup on Wednesday.

The American horse, based in England, blitzed the field to claim the 137th edition of the race and put itself into firm contention for the Melbourne Cup.

The seven-year-old gelding, ridden by Craig Williams, took the lead with 250 metres to go and finished two-and-a-half lengths ahead of Interpretation in second and Muramasa in third.

Williams, fresh off riding Bella Nipotina to win The Everest in Sydney last Saturday, now has a sixth Geelong Cup to add to his impressive career. 

Pre-race favourite Unusual Legacy was pulled up by jockey João Moreira after barely 200m, with fears it had broken down.

Broadcaster Racing.com reported Unusual Legacy was able to walk onto the float under its own power before being taken for assessment. 

English trainer Brian Ellison was full of praise for the victorious Onesmoothoperator after claiming the Geelong Cup.

"I've been here a few times and had a few bits of bad luck, but this horse has been brilliant," he told Racing.com.

"I said to Craig [Williams], 'He's not your normal stayer, he's got lots of speed.'

"He's got a good turn of foot and [Williams] gave him a great ride."

Three horses, Media Puzzle (2002), Americain (2010) and Dunaden (2011), have gone on to win the Melbourne Cup after saluting in that year's Geelong Cup.