With premiership leader Beau Mertens in high demand, trainer Luke Oliver was on the front foot to secure the apprentice to ride Hot Ruby in the David Bourke Provincial Plate at Flemington.

Hot Ruby heads into Saturday off a close-up fourth last-start at Moonee Valley in a fillies and mares 1500m race with another apprentice, Jordan Childs, aboard.

Mertens gets back aboard with Hot Ruby to carry the minimum 54kg in the 1600m race restricted to horses who have competed in at least three races outside the metropolitan area in the past year.

"Beau won on her two starts ago at Flemington and he's going so well this season," Oliver said.

"He just seems to have the knack of putting them in a winning spot in the run and he can ride the 54 kilos easily."

The Caulfield trainer got in early to book Mertens who leads Craig Williams by one win in the Melbourne premiership.

"I reckon it was the day after she ran at Moonee Valley when I booked him for this race," he said.

"I think you've got to get in quite early to get him."

Mertens went to Pakenham on Monday to trial Hot Ruby on the synthetic track over 1400m, with both trainer and jockey happy with the hit-out.

The trial kept the mare ticking over and Oliver said there was another reason for taking her there five days before the Flemington race.

"When she won at Caulfield impressively (in February) she was racing off an eight-day break there," Oliver said.

"I just think she probably races better on a short back-up.

"That's why I thought, with three weeks between runs, we'd give her that trial."

Formerly trained by Brian Cox, Hot Ruby has had 14 starts for the Oliver stable this season beginning with a second at Stawell last October.

Despite a long campaign, Oliver says the mare is showing no signs of training off.

"She certainly feels like she's almost peaking for this run, rather than racing like a tired horse," he said.

"She's going there as well as we have taken her to the races. She'll run to her absolute best."