Prebble was overjoyed to win his first Cup.
"It's my life dream to do it,'' he said.
He said his horse was checked by other runners soon after the start but he was always confident.
"I pressed him a bit soon but it's hard to wait here when you've got so much power underneath you.
"I was very confident they weren't going to pick him up when I let him down and he ran all the way through the wire.''
It was a fourth Cup victory for owner Lloyd Williams, who won previous Cups with Just A Dash (1981), What A Nuisance (1985) and Efficient (2007) but was not at the track to see his horse win.
"He puts a lot into racing and he's a very good supporter of mine,'' Prebble said.
"He's never here. He's going to be at home enjoying it. It's lovely.''
Williams's son Nick was ecstatic after accepting the trophy from Camilla, Duchess of Cornwall.
"We put a lot of money in and a heck of a lot of effort so to get this result today is terrific,'' he said.
"God bless everyone who wrote him off.''
Fiorente was the third Cup runner-up for trainer Gai Waterhouse, who previously trained Te Akau Nick (1993) and Nothin' Leica Dane in 1995.
It was not a good day for the only two locally bred horses in the race.
Niwot was 15th and Ethiopia was last.
- AAP
