A yearling half-brother to world champion Black Caviar has sold for an Australian record price of $5 million.

Lot 131, by champion sire Redoute's Choice out of broodmare Helsinge, was the star lot of the Inglis Easter Yearling Sales, which opened in Sydney on Tuesday.

The blue-blooded colt was knocked down to a syndicate from BC3 Thoroughbreds, which bought Black Caviar's half-sister last year for $2.6 million.

The viewing areas in and around the ring at the Newmarket sales complex were at near capacity as bidding came down to a duel between BC3 and Adam Sangster from Swettenham Stud.

Bidding opened at $2 million and advanced in $500,000 increments to $4 million; from there it was $100,000 per bid before the hammer came down.

What price a champion? While Black Caviar's half-brother attracted a record $5m bid in Australia, race horses in the USA have sold for almost three times that amount...but have not always lived up to their hype. The Green Monkey: foaled 2004, sold $15.3 million (2006)

The two-year-old colt was sold for a world record price and made his debut at Belmont Park in 2007 finishing 3rd. In his second start, at the same course, he finished 4th. He was officially retired in February 2008 after failing to break his maiden. Career earnings $6,800. Seattle Dancer: foaled 1984, sold $12.5 million (1985)

The most expensive yearling ever sold at auction finished 3rd in his April 1987 debut before winning the Group 3 Gallinule stakes and the Group 2 Derrinstown Stud Derby Trial. In his next start, at Longchamp racecourse in Paris, he finished 6th. Seattle Dancer ran his final race at the same course running 2nd. Career earnings $162,000. Meydan City, foaled 2005, sold $11.21 million (2006)

The second most expensive yearling to be sold at public auction broke his maiden at Newmarket in 2008 ridden by Frankie Dettori. He made seven starts in his career with just one other win and a third. Meydan City was retired in 2009 with a total career earnings of $35,000.

The previous national record of $3 million was held by colts sold at the Inglis sales in 2006 and 2007.

The Australasian record had been the $NZ3.6 million paid at New Zealand's Karaka sales for a Zabeel colt, who raced in Australia as Don Eduardo and went on to win the 2002 AJC Derby.

Helsinge's last two yearlings to go through the sales were a colt by Casino Prince - champion three-year-old All Too Hard - and BC3's unraced Redoute's Choice filly named Belle Couture.

BC3 chairman Bill Vlahos said stable clients had put up most of the money but a small share was still available - the smallest share offered would be 5 per cent ($250,000).

"As soon as Belle Couture told us she wasn't going to let the family down, we really started looking at this horse," Vlahos said.

"We're just pleased that the purest of Australian blood stays in Australia."

Vlahos said his vets had given him the green light despite some respected judges putting a knock on the horse.

"We've got some good clients, there's also some of our money in that too, so we're not going to be headless in making decisions like this," he said.

"Our owners trust us implicitly."

Sorry, this video has expired Black Caviar's half-brother sells for record price ( Scott Bevan )

The stallion potential of Lot 131 was a big factor in his record price.

All Too Hard, a winner of three Group Ones including the Caulfield Guineas, was bought for $1,025,000 in 2011 and sold last year to Vinery Stud in a deal worth more than $25 million.

Former top jockey Simon Marshall, now BC3 sales manager, said the colt would not be rushed onto the racetrack.

"We know how good Belle Couture's going and it is just great to get the full set with this colt," he said.

"He's typical to the family and has a lot of growing to do, so he'll let us know when he's ready to rock and roll."

No decision has been made on a trainer, although Marshall said Black Caviar's trainer Peter Moody and All Too Hard's trainer John Hawkes would be considered.

The day's other sales were highlighted by Lot 123 - a half-brother to Caulfield Guineas winner Starspangledbanner - which was knocked down for $2.4 million.

Other seven-figure lots were colts by Fastnet Rock ($1.5 million) and Snitzel ($1 million).

The yearling's illustrious relation was also keeping a close eye on the action:

$5 million for little brother. Congrats @gilgaifarm @inglis_sales @bc3thoroughbred — Black Caviar (@blackcaviar2006)

Nervous wait

Meanwhile, Sydney's recent wet weather has the Australian Turf Club facing a nervous wait to see if Black Caviar goes for win number 25 at the Derby Day meeting on Saturday.

The mare's connections are adamant she will not contest the $1 million TJ Smith Stakes (1,200m) if the Randwick track is heavy.

Showers at the track on Tuesday have the track rated as a heavy 8, but ATC spokesman Matt Rudolph says fine weather forecast for later in the week is expected to help dry out the track.

"Just talking to the track manager and it's a heavy track, but with the rain at the moment and the weather forecast ahead of Saturday, it's actually ideal conditions."

Black Caviar worked in Melbourne on Monday and Moody described the speed of her gallop as "scary".

The great mare is one of 17 horses nominated for the Group One TJ Smith, a race she won two years ago.

Meanwhile, the barrier draw for Saturday's feature event, the $1.5 million Australian Derby, was conducted on Tuesday morning, with odds-on favourite It's A Dundeel drawing barrier 8.