Faith in his own judgment and a piece of dubious racing wisdom led trainer Robbie Laing to spend $4500 on a horse he now regards as a Derby prospect.

Polanski, a son of the ill-fated stallion Rakti, scored an upset win in Saturday's Routley's Handicap (1440m) at Caulfield, earning himself a rest and offering the promise of something much better.

Laing said he had been keen on the stock of Rakti, even when others were not.

"I'd always wanted to train a Rakti and when he died I was even more keen," Laing said.

"It often happens that after they die they produce a good one."

Long-time client Ken Coram and his wife Henny spotted Polanski at the Melbourne autumn sale and Laing got him cheaply enough to take the chance to indulge his theory on the stallion.

"He was a diamond in the rough at the sale," he said.

"But he walked well, he had attitude ... and now he's won in town."

Polanski ($21) sat on the back of the heavily tried favourite and leader Gracious Prospect ($2.60), coming off the fence at the 200m and asserting himself after a short struggle to score by a half neck with Great De Here ($3.60) a distant third.

Laing said he would normally have used Saturday's race as a lead-up to the Gibson Carmichael Stakes, a traditional late-season test of juvenile staying potential.

But the race has been switched to a new date so Laing will turn Polanski out and with a view to aiming him at the Victoria Derby in the spring.