Gai Waterhouse made history in 2001 with the trifecta in the Golden Slipper and sees no reason why she can't do it again.

Leading her trio on Saturday is Overreach, the dominant $2.20 favourite for the $3.5 million Slipper (1200m) at Rosehill, the world's richest race for two-year-olds.

Overreach will start from the inside barrier but Waterhouse is just as enthusiastic about Sweet Idea and Whittington who drew barriers four and eight respectively.

Barrier one is not always considered ideal given the mad dash to the first turn and jostling for position but Waterhouse, who collected her fourth Slipper last year with Pierro, said she was not worried.

"Luck plays a big part in the Slipper," she said.

"I feel very comfortable with my group.

"Overreach has drawn barrier one which I was very concerned with last year with Pierro but the quickest way to the winning post is along the rails."

Waterhouse likened Sweet Idea to 2001 Slipper winner Ha Ha who beat Excellerator and Red Hannigan. Like Ha Ha, Sweet Idea will be ridden by Jim Cassidy.

"Sweet Idea is the most professional filly I've trained since Ha Ha and after Saturday we will know if she's as good.

"And Whittington has just progressed wonderfully. He's come along in leaps and bounds."

Waterhouse said she hadn't paid much attention to the rest of the field with her focus firmly on her runners.

"Just stick with my three and you won't go wrong," she said.

Overreach replaced Villa Verde as the Slipper favourite when she won the Widden Stakes in February.

Villa Verde is the only horse to have beaten Overreach which she did in the Debutants Stakes in October at Caulfield.

They met again in last month's Reisling Stakes with Overreach scoring a comprehensive win over the Shaun Dwyer-trained filly who drifted even further in the markets on Tuesday to $13 after coming up with barrier 17.

But her jockey Michael Rodd is keeping the faith.

"It's not the end of the world," Rodd said.

"She is very good from the barriers so hopefully we can come across and end up three deep with cover."

Ruud Awakening's bid to become the first New Zealand-trained horse to win the Slipper also suffered a blow with Craig Williams's mount to start from the outside gate.

Her trainer Stephen Marsh drew the barrier and admitted she would need luck.

"I've only got myself to blame," he said.

"We need luck and a bit of rain would even things up.

"But that's why we pay Craig the big money, to work it out."

Ruud Awakening, who counts All Black great Colin Meads among her owners, eased slightly from $12 to $13 but the TAB's Glenn Munsie said a win by the filly was still the worst result for his firm.

Like Waterhouse, Sheikh Mohammed's Darley operation has three runners - Sidestep, Kuroshio and Guelph - with Sidestep the second favourite at $10.