Shamus Award only made it into the Cox Plate field when the headline mare Atlantic Jewel was scratched.
It was the only piece of fortune the colt needed, according to O'Brien.
"Today we just got our chance to get out there and make our own luck and show what a good colt this is," O'Brien said. "He could have easily been a Guineas winner and a Cox Plate winner, but we're pretty happy to take the Cox Plate."
New Zealand star It's A Dundeel finished unplaced after being trapped wide for most of the race.
"Extraordinary! He's back!"
That's how one punter summed it up as Bart Cummings' last hope for a Melbourne Cup start, Precedence, powered home to win the group two Moonee Valley Gold Cup yesterday.
The race was a "last chance saloon" for three other horses in the race - Tanby, Sneak A Peak and Shoreham - for a Cup entry, but it was Bart Cummings, in partnership with his grandson James, who prevailed.
The king has won the Melbourne Cup 12 times and Precedence is his only chance this year for more glory, and the first with his grandson.
Before the win, Precedence was 44th in the order of entry for the Melbourne Cup with 52kg and his chances of running now depend on chief handicapper Greg Carpenter.
Carpenter will announce the weight penalty for Precedence tomorrow.
With Craig Williams on board, Precedence ($7.50) ran a commanding race, happy to sit in the back half of the field of eight. Williams made his move at the turn of the 2500m race, steering the eight-year-old gelding to the front, and moving away from the pack despite a charge from Shoreham ($5).
He won by 1 lengths with Gotta Take Care another 1 lengths away in third.
Williams was in no doubt about Precedence, part-owned by Sir Patrick Hogan who stands his sire Zabeel at his Cambridge Stud, lining up for what would be his fourth Melbourne Cup. His best finish was an eighth in 2010.
"He's a big chance, without a doubt," Williams said. "He's got the Bart Cummings factor and it would be great for the 2013 Melbourne Cup if Bart Cummings and James Cummings had a run."
James said his grandfather would make the trip from Sydney for the race if Precedence was given a penalty that would get him into the Cup.
"We'll be more than happy to take them on," James said. "Precedence has got a zest for it and he's got some unfinished business. He's by Zabeel and it's a great pedigree for horses that go better with age."
Carpenter said the cut-off for the Cup would be around 53kg to 53.5kg.
He said if Precedence was given a one kilo penalty he would still be vulnerable in the ballot and would need horses above him not to accept. AAP
