Jockey Oliver, returning from a 10-month ban, rode the winner for trainer Waterhouse who is married to a man once warned off the nation's race courses, and who is fighting to clear her own name after a track-side argument with millionaire owner John Singleton.
Fiorente won the Cup with a sustained burst from midfield in a race tinged with tragedy after claiming the life of French mare Verema.
For Waterhouse, the queen of the local racing scene, victory in the $6 million race came 20 years after she battled her way into what until then was predominantly a men's only game.
Even her bid for a trainer's licence was delayed at the time by a protracted battle with authorities who denied her because her bookmaker husband Robbie had been warned off over the Fine Cotton affair.
"It is every trainer's dream and yes, it has been a burning desire to win," she said of her first Cup victory.
"I didn't want to let people down. I kept saying to Rob 'God I hope we win it'."
Daughter to two-time Cup winning trainer TJ Smith, her Cup win came six months after she was dragged into an unseemly track-side spat with Singleton.
He sacked her as his trainer after More Joyous flopped in the All Aged Stakes at Randwick in the autumn and Waterhouse is still appealing a stewards fine stemming from the race.
Fiorente's three-quarter length victory in the Cup also came only hours after Waterhouse was hauled before stewards to be quizzed on a treatment given to her other Cup runner Tres Blue, who finished second last.
She is still facing an inquiry over that incident.
While Fiorente's win focused much-deserved attention on Waterhouse's abilities, it also added another twist to the chequered racing life of jockey Oliver who won previous Cups on Doriemus in 1995 and Media Puzzle in 2002, just days after the death of his hoop brother Jason in a trackwork fall.
This time last year Oliver found himself at the centre of a massive scandal after being reported to the racing integrity commission for betting on another horse in a race in which he was riding.
Oliver put $10,000 - which he said was his first ever bet - on the winner of a Moonee Valley race.
But it was the subsequent deal he struck with authorities that proved more controversial.
Oliver was allowed to ride until the end of the spring carnival and then, in return for a guilty plea, received a 10-month ban widely viewed as grossly lenient.
Oliver said he was looking forward to the future and had moved on from the scandal.
"I did the crime and I've served my time. It's time to move on," he said.