Gai Waterhouse predicted Pierro would win the Golden Slipper six months ago and the colt proved up to the task in the world's richest juvenile race.

On October 1 last year, Gai Waterhouse declared Pierro the Golden Slipper winner.

Six months after his winning debut in the Breeders' Plate the prediction came true with the colt giving the trainer her fourth win in the world's richest race for two-year-olds at Rosehill on Saturday.

"In the heat of the moment you say things you probably shouldn't but I knew that this was a special colt," Waterhouse said after the Slipper.

"The improvement he had made from his first few gallops to his first race was amazing."

Waterhouse sent out five runners in the 1200m dash to take on Melbourne filly Samaready, the Blue Diamond winner and the $2.80 favourite.

Pierro ($6.50) was in a beautiful position up on the pace after jumping from barrier one with Snitzerland ($26) wresting the lead from Faustus.

Snitzerland put a couple of lengths on the field rounding the turn and raced away to look as if she would give trainer Gerald Ryan his first Slipper.

But Nash Rawiller stoked Pierro up to give chase and slowly but steadily wore the filly down to put a long neck between them on the line.

Samaready gave chase after a slow start but could only get to within 1-1/2 lengths of the runner-up with Queensland filly Doubtfilly a gallant fourth.

"Gai Waterhouse said six months ago this horse was going to win the Golden Slipper," Rawiller said.

"I shook my head and walked away. She's a genius.

"He made his own luck today.

"He jumped well and it went through my mind early to lead but there was a bit more pressure so I was happy to sit off them.

"I just wanted to sit there as long as I could and wait for it to happen.

"Corey (Brown on Snitzerland) has rolled off a few and it was just game over then.

"I knew if it came down to a dogfight he was going to be too good. He's just such a talented colt."

Pierro, a colt by Lonhro out of Miss Right Note, cost $115,000 at the Magic Millions weanling sale and was later sold as a yearling for $230,000.

For about 300 metres, Brown thought he was going to get his hands on his first Slipper trophy.

"I just had the easiest run in front," he said.

"She travelled really sweet.

"I thought I was on the winner. It took a good one to beat her."

Ryan, who trained Paint to run second to Merlene in 1996, cheered Snitzerland home in defeat.

"She's run her guts out," he said.

Melbourne trainer Mick Price was also proud of his filly but disappointed she couldn't win.

"She ran super," Price said.

"Craig (Newitt) said she reared up at the barrier.

"I thought about the 600 she was a chance.

"It would have been nice if she could have run them down.

"It would have been nice if she had had the winner's barrier."

There were few hard luck stories to come out of the race with Waterhouse to press on to the Sires' Produce Stakes and Champagne Stakes in an attempt to emulate her 2004 feat with Dance Hero.

A crowd of almost 30,000 came to Rosehill for the Slipper which was run in sunshine on a good-rated track.