Imperialist remains in contention for a start in the Queensland Derby (2400m) despite lingering doubts about his stamina, following his surprise victory in Saturday’s Rough Habit Plate (2000m) at Doomben.

The Chris Waller-trained three-year-old turned his form around dramatically after a disappointing run in the Queensland Guineas, finishing strongly to claim the Rough Habit Plate and thrust himself back into Derby calculations.

However, Waller admits the step up to 2400m is a concern after Imperialist failed to stay the trip when finishing well back in the ATC Australian Derby last month.

“He brought some good form to Sydney from Melbourne then just didn’t quite stay the 2400 in the Derby,” Waller said.

“We’ve got a little bit of concern about the 2400.

“I think the Churchills are more speedier horses so that’s the challenge we’ve got to deal with in the next two weeks.”

Sent out at $61 by online betting sites, Imperialist surprised punters after finishing down the track in the Queensland Guineas (1600m) at his previous start. A gear change and a positive ride from jockey Tommy Berry proved key to the upset win.

“We tried blinkers (in the Guineas) and it just didn’t work. He missed the start,” Waller explained.

“So we took them off and suggested to Tommy we ride him a bit closer. He had a nice soft time up in front and it just sparked a bit of interest.”

Berry said the gelding responded well to being ridden more positively and backed Waller to prepare the horse for the Derby distance.

“If he says he will get him to stay again, he will get him to stay,” Berry said.

“He is the best staying trainer that’s going around.”

Following his Rough Habit win, Imperialist has firmed from $101 into $15 for the Queensland Derby, while King Of Thunder, who ran third on Saturday, remains favourite at $6.

Punters looking to back Imperialist or track Queensland Derby markets can do so via top Australian betting sites.