Glen Boss has revealed how he is drawing on the events surrounding his first two Golden Slipper wins as the inspiration for a hat-trick in the world's richest race for two-year-olds.

Boss has perfected the art of making the most of a late call-up to win the Slipper.

He took the ride on Flying Spur in 1995 when Jimmy Cassidy became embroiled in the jockey tapes affair 24 hours before the race.

And he capitalised on more misfortune when he flew in from Hong Kong to replace the suspended Blake Shinn on the 2008 winner Sebring.

"Flying Spur was my first major winner and really sent my career on an upward spiral," Boss said.

"He'll always be special."

Getting the ride on the Hawkes Racing-trained Headwater evokes similar memories for the jockey who rides out of Melbourne.

Headwater fell from Golden Slipper favour when he was beaten into the minor placing after a wide passage in the Todman Stakes.

The colt will line up at double-figure odds at Rosehill on Saturday with Boss on top for the first time.

"He was the favourite for the Slipper but had dropped off the radar a bit after that race," Boss said.

"John (Hawkes) couldn't understand why he ran like he did the other day but he must have really liked what he saw on Tuesday because he rang me straight away to say I've got the ride.

"It was a confident call."

Boss reasons Hawkes and owners the Vinery Stud syndicate must be certain Headwater is at the top of his game to run the horse because there is no way they would want to diminish his value as a sire.

"He's got speed and the right horses drawn around him to run well," Boss said.

Hawkes Racing will also have Blue Diamond Stakes placegetter Lake Geneva as a more than able back-up for Headwater.

The Gai Waterhouse-trained Vancouver continues to hold favouritism over Exosphere and they account for most of the percentage in a market that has barely changed in the past 48 hours.

Waterhouse's husband Robbie declared Vancouver an odds-on chance before the barrier draw and the trainer has the unbeaten youngster as the clear top pick of her three runners.

She said the time Vancouver ran to win the Todman compared to that clocked by stablemate English in her Reisling Stakes success made a compelling case for the favourite.

"I remember dad (T J Smith) saying to me years ago you only have to worry about one thing with two-year-olds and that is what time they ran," Waterhouse said.

Vancouver's overall time for the Randwick 1200m was 1.36secs faster than English's - a difference that equates to eight lengths over the distance.