There will never be another Winx but that hasn't stopped a baby sister already trying to match her famous sibling.

The mother of Winx, Vegas Showgirl, gave birth to the filly by late Japanese stallion Deep Impact, about 11am on Tuesday at Segenhoe Stud in the Hunter Valley.

"I've probably seen about 20,000 foalings, the only one I've ever seen to jump up on their feet straight away is Winx, and this is the second," Segenhoe Stud's general manager Peter O'Brien told AAP.

Winx had one of the greatest careers in Australian horse racing with 37 wins - 25 at Group One level - earning her the title of world's best.

But it doesn't come cheap to replicate a star racehorse, with breeder-owner John Camilleri banking on a number of factors pulling through.

"He took a big gamble, it's effectively a $400,000 exercise," Mr O'Brien said.

Last July Vegas Showgirl flew to Japan's northern island of Hokkaido to mate with Deep Impact.

At 16 years old it was the last year she would be fit to travel, while Deep Impact was also of age.

The prized stallion who has sired champion racehorses all over the world, died in July this year.

"We're hoping all those stars align and she's even five per cent as good as Winx," Mr O'Brien said.

For thousands of years, mares have given birth at night to avoid predators, with about 95 per cent today following this tradition.

According to Mr O'Brien, a morning foaling is "highly unusual".

Winx was also born in the morning, about 8am.

While Mr Camilleri doesn't dream of selling his new prize, if the foal was to go for sale Mr O'Brien estimates the filly would make a minimum of between $3 million and $5 million.

On Wednesday, with the sun on her back, the athletic filly has been running tight circles around her mother.

Over the next 20 or so months she will stay at the stud farm before Mr Camilleri decides who will train her.

Vegas Showgirl's two-year-old Covent Garden has just been given to Winx's trainer Chris Waller, while the dam herself will soon head to Yarraman Park to meet her new mate I Am Invincible.

The champion sire doesn't throw big foals, and is therefore a good physical fit for leggy Vegas Showgirl. For this reason he's also been matched with Winx.

"I was speaking to one of Winx's owners last night and we were saying we hoped it wasn't on the same day, it could get a bit weird," Mr O'Brien said.

"Mother and child, same boyfriend."