A fellow jockey's misfortune has given Paul King an opportunity to have his best day on a Sydney racetrack as he answers an SOS from trainer Gai Waterhouse.

In circumstances similar to his win on Flamboyant Lass for Waterhouse at the corresponding city meeting last year, King has picked up an impressive book of rides at Canterbury on Saturday.

The former Perth jockey is on three early favourites including the Waterhouse-trained Bold Adventure in the James Boags Handicap (1550m).

King rode Bold Adventure when the colt made a winning debut at Kembla Grange but Adam Hyeronimus was expected to take the Canterbury ride.

Hyeronimus injured his collarbone in a race fall last week, clearing the way for King to continue his association with a three-year-old Waterhouse is hoping to turn into a Derby prospect.

"Adam got hurt the other day and everyone else is up at the Gold Coast," Tulloch Lodge spokesman Mark Newnham said.

"Paul was a logical replacement. He understands how Gai likes them ridden and he knows the horse."

As a son of Savabeel, Bold Adventure is bred to stay and Newnham says Waterhouse is keen to explore Classic options.

"In both his trials he had shown good speed and at Kembla he showed that he had good cruising speed," Newnham said.

"Gai thinks he might develop into a Derby horse and there are options.

"If he impresses again on Saturday, she might decide to press to the Australian Derby or he might have a few weeks off and that brings the South Australian Derby and Queensland Derby into the equation."

King will also ride topweight White Dove for Waterhouse in the TAB Rewards Handicap and Newnham said the mare's record at Canterbury would count for a lot.

"She's had a couple of wins at Canterbury and she was just a touch unlucky the other day (at Rosehill)," he said.

"Her form has been solid without winning this time in but her form at Canterbury has been good."

King will ride two-year-old Detective for the Snowden stable in the Schweppes Handicap and the colt is favourite to make a winning but belated start to his second campaign.

Detective lost a tooth when he lunged at the starting stalls and was withdrawn at Randwick on Boxing Day.

King has also been booked to ride Rule The River, favourite for the TFE Hotels Handicap.

Rule The River is also entered for the Takeover Target Stakes at Gosford on Friday and trainer Anthony Cummings' preference is to run the in-form mare in the provincial Listed sprint.