Red Cadeaux came in second, with Auckland Cup winner Who Shot Thebarman placing third.
But favourite Admire Rakti has died after finishing last in the race. It won the Caulfield Cup in brilliant style last month, and today raced near the lead formost of the 3200-metre journey.
As it rounded the final bend the horse was clearly under pressure and dropped back through the field sharply.
He finished 25 lengths behind the second-last horse.
Auckland Cup winner Who Shot Thebarman was the first Australian-trained horse to finish, making ground along the inside to take the minor placing ahead of Signoff.
Favourite Admire Rakti, aiming to complete the Caulfield Cup-Melbourne Cup double, raced in second place but was beaten at turn and dropped right out.
"There was no catching that winner -- it won quite easily and just accelerated at the end, nothing could go with it."
The two most backed horses were New Zealand's Who Shot Thebarman, which came in third, and Japan's Admire Rakti, which came in last, and later collapsed and died after the race.
"Who Shot Thebarman did a great job, he was against the best in Australia and the northern hemisphere -- all round he finished third.
"It was a great honest race by Who Shot Thebarman."
The biggest bet made on this year's winner, Protectionist, was $5000 to win.
At $7.50 to win, the punter got a return of $37,500, Mr Stafford said. The bet was made online.
"There are plenty of winners out there that have had a bet today."
New Zealand's Melbourne Cup celebrations have been in full swing for much of the day - with punters around the country crowding the nation's racecourses, bars and restaurants.
In Auckland, Ellerslie Racecourse attracted its biggest crowd in five years for a Melbourne Cup day, with 5000 racegoers expected throughout the day.
Takapuna mother-of-three Claire Hahn won best dressed woman in the Sofitel Melbourne Cup Award in a stylish top and mid-length patterned skirt combo.
Mark Wallbank, who owns several Auckland restaurants including Ponsonby's Blue Breeze Inn and Moo Chow Chow, took out the men's competition in an outfit "thrown together" this morning.
Mrs Hahn, who is a milliner designer, stuck to neutral colours for her outfit, completing the look with strappy heels, a beige clutch and hat she made herself.
Mr Wallbank said he tried a few outfit combinations on this morning before settling on his winning ensemble.
The Melbourne Cup enthusiast, who spends every other race day at Ellerslie, wore a bow tie for the first time this year. He also threw in a cane and hat.
The Ascot Ave venue was also hosting 10 thoroughbred races of its own.
Chief executive Cameron George said the day had started well, and racing fans were enjoying better weather than forecast.
"Everything is great and the crowd is building, we will hit the 5,000 mark," he said. "It's the best it's been for the last five years.
"People want to be close to the action where you can see horses...so I am sure that's a draw card."
Big winners
* A $5000 bet on winner Protectionist, which was paying $7.50, won $37,500.
* A $1000 bet on winner Protectionist, placed in October when the horse was paying $51, won $51,000.
* A $10,000 bet on Araldo to finish in the first 10, paying $2.30, won $23,000.
* A $5000 bet on an international trainer to win the race, paying $1.95, won $5000.
* There were approximately 650,000 bets placed on the Melbourne Cup.
* TAB turnover for the 154th Melbourne Cup race was just over $10 million, surpassing last year's turnover by approximately $1 million.