Hall of Fame trainer David Hayes' Caulfield Cup "miracle" will sink in when the winning owner's cheque lands in his bank account.

Even Hayes was surprised when 50-to-one shot and last-minute entry Boom Time won the $3 million race, the world's richest turf handicap over 2400 metres.

Hayes had his eyes on his three more fancied runners, who he'd backed, when son Ben elbowed him and yelled "Boom Time Dad".

"I can't believe it. A miracle's happened," a shocked Hayes said.

It was Hayes' third Caulfield Cup win as a trainer, but first in partnership with Ben and nephew Tom Dabernig and first as an owner.

"To do it with my family is just fantastic, and then to be the only owner, it's just incredible," Hayes said.

Hayes bought the six-year-old horse from his good friend Kim Loxton earlier this year.

"He had to sell all his horses. This horse had nowhere really to go. I love the horse so I took him," he said.

"I thought he'd pay his way, but he's done a lot better than that."

Team Hayes only decided to enter Boom Time after one-time Cup favourite Admire Deus was scratched from the race after suffering a life-threatening injury.

"We were doing all the maths on how much it was going to cost and whether it would be too much," he said.

"We thought let's have a go."

Hayes said sharing a Caulfield Cup win with his family was special.

"Ben was quite emotional. He probably just saw a bit more of his inheritance go up, I reckon," he joked.

Jockey Cory Parish was also pinching himself after his first Group One win.

Parish was originally meant to be working in Sydney on Saturday but quickly took up the opportunity to ride Boom Time before a 30,000-strong crowd at Caulfield.

Boom Time may now head for the Melbourne Cup.

"I'd say if he's well then why not go for the dream. You don't get many opportunities as an owner, do you?

"My greediness has come out - a greedy owner," Hayes quipped.

Does snaring the Caulfield Cup as an owner rate as the most important win of his career?

"It will be in a month when I look at the bank book."