Every state and the Northern Territory will each have one official representative who can earn points towards the national competition.

Singapore will also be represented for the first time but New Zealand, after indicating it would compete, is a late withdrawal.

With the Elwick heat attracting a capacity field of 14, another six apprentices have been invited to make up the numbers.

Although she is not officially representing SA, Teagan Voorham will return to her home state to ride in the heat and seven other races.

Voorham is fifth on the metropolitan jockeys' premiership in Adelaide with 14 wins and has won 33 races statewide this season.

Apprentices eligible to earn points in the first round are Ianish Luximon (Tas), Dan Morgan (NT), Dakota Graham (Qld), Carleen Hefel (Vic), Sophie Logan (SA), Beaux Banovic-Edwards (WA), Brandon Griffiths (NSW) and Shafrizel Bin Saleh (Singapore).

There are further heats at Ascot, Doomben, Sandown and Murray Bridge.

Tasmania was runner-up in the series in 2017 and 2018.

Colby Sanz scored a tough win in the Tasmanian Guineas in Hobart on Sunday night but trainer Kent Rattray believes his best is still to come.

"He's very strong and we've always thought he'd be at his best when he gets over longer distances," Rattray said. "He willl love the 2500m of the Tasmanian Derby.

"It depends what comes from the mainland but he beat a couple of very nice horses tonight and we'd love a nice draw in the Derby so he can pop on top again."

Rattray said that Colby Sanz relaxed when he found the front, in contrast to his previous win at Devonport when he raced fiercely in the death.

Meanwhile, a hard run ended the eight-race winning streak of promising four-year-old The Shallows in the Rating 70-79 Pace.

The Heath Woods-trained gelding was caught wide before working to the death and was left a sitting shot for Blackbird Power who came off his back to score easily.

The Shallows wouldn't have lost any admirers with his tough effort while Blackbird Power again showed he can match it with the best on his day.

"It was soft at the finish," said winning driver Adrian Collins. "This horse can mix his form a bit but when he's hot, he's hot."

Consistent galloper Beaufort Lad has been retired due to injury after a career that netted 12 wins and almost $200,000.

The eight-year-old also had 18 minor placings and averaged $3580 in stakes per start.

Part-owner Darren Simmonds said Beaufort Lad had been a wonderful horse who tried hard every time he went to the races, loved a dog fight and knew "when to stick his big head out."