A horse trained like a sprinter will be out to confirm her worth as a stayer at Randwick on Saturday.

Country-trained Declasse will take her place in the appropriately named Stayers Cup on the back of an unorthodox training regime.

"All I do with her is give a lot of trot and cantering work," trainer Brett Thompson said.

"It's usually just one lap of the track and her equivalent of a fast morning might be two laps.

"Keeping her fresh like you would with a sprinter, you can have your doubts taking her to the races but she is obviously just a natural long-distance horse."

Thompson switched his approach to Declasse's training when she lost form in the middle of what has turned out to be a 15-start campaign.

"I always thought she would make a stayer but I became really frustrated with her and I nearly gave up on her," he said.

But Declasse, a $5,500 weanling purchase from global breeding enterprise Darley, improved enough to give Thompson his first provincial winner when she scored over 2600m at Gosford last month.

And it was her last-start fourth placing to Cup rival Tognetti at midweek city grade at the same track which convinced Thompson to press on towards a 3200m start.

"She gave the impression she is looking for two miles," he said.

"The feeling is she might be out of her depth but you never know until you try them."

Declasse is one of the outsiders in a race where it is another mare, the Victorian-trained Unchain My Heart, who heads a wide betting market at $4.60.

Unchain My Heart is a last-start winner over the distance after being saved for a final 250m finish to win the Andrew Ramsden Stakes at Flemington.