Trainer Bryce Heys has had his eye on the Darley Classic since before Spieth had his first race start.

Spieth lines up in Saturday's Group One sprint coming off a last-start win at Randwick.

The Warwick Farm-based Heys kicked off Spieth's career in Melbourne last spring, but was already thinking 12 months ahead.

"For one reason or another things didn't work out," Heys said.

"Twelve months ago I had a lot of belief in the horse's ability.

"I had a frank discussion with everyone to say we could get into this race if you let me go back to the drawing board with him and teach him how to be a racehorse."

Spieth bumped into Secret Agenda at Sandown in September last year before an easy win at Pakenham.

He was then turned out for a spell after running seventh in the Caulfield Guineas Prelude.

Spieth returned in the autumn with a 10th behind Japonisme in the Arrowfield Sprint at Randwick before winning four consecutive races.

Included in that sequence was a straight-track victory over 1100 metres at Flemington that was part of the plan heading towards Saturday's race.

"The racing and the winning has helped his confidence in terms of maturity," Heys said.

"But I was never getting ahead of myself.

"Not at one stage did I think 'I can't wait to get down and run in that Darley Classic' but that was definitely my long-range plan if he could do what he's been doing.

"I was just worried about putting him in the right races and doing the right thing by the horse."

Heys kept Spieth in Sydney for a first-up assault on the City Tattersalls Lightning Stakes at Randwick knowing there was improvement to come.

But Heys knows Saturday's Group One race is a tough assignment.

"Everyone in our camp has got their feet firmly on the ground," Heys said.

"It's been a long range plan that we were going to have to run against the big grey horse (Chautauqua) but even with him not there we know how hard it's going to be."