Veteran jockey Robert Thompson has extended his perfect record with Valree after she made her customary slow start in the Highway Plate at Rosehill.

Thompson knew what to expect with the four-year-old on Saturday so didn't panic before conjuring a rails run to pip fellow $5.50 chance Volpe in the 1500m race.

The mare scored by a long neck to make amends for an unlucky last-start fourth, with Irish apprentice Robbie Dolan at Newcastle last month.

"She was probably a certainty to be beaten but the kid was having his first ride on her, she copped interference at the start and over-dramatised it, as she does," trainer Rod Northam said.

"She still probably should have nearly run second but it's nothing against him. She's a bit quirky but Robert's got the key to her at the moment."

Scone-based Northam said Valree would now step to 1800m for the first time after her third win from nine starts and first metropolitan race.

He said he had learnt to live with Valree's tetchy, sluggish starts.

"She's a difficult horse. She has jumped a couple of times but she doesn't like being crowded. She doesn't like other horses around her," he said.

Central Witness ($9.50) was 1-3/4 lengths back in third.