Star mare Imperatriz will bid to keep her unbeaten record at Moonee Valley intact when she seeks a second win in the William Reid Stakes.

Imperatriz won the 1200m Group 1 sprint last year before going on to take the Group 2 McEwen Stakes (1200m), the Group 1 Moir Stakes (1000m) and the Group 1 Manikato Stakes (1200m) last spring.

The Mark Walker-trained mare is the $1.75 favourite to continue her streak at The Valley on Saturday after drawing barrier 10 in the 11-horse field.

Ben Gleeson, Walker's assistant trainer based at Cranbourne, said the stable would have liked to have drawn in a shade, but it would now be up to Opie Bosson to weave his magic on the mare.

"He knows her so well and he's a world-class jockey," Gleeson said.

"I think it is better to be drawn wide than inside.

"It will be good to get some cover and I think that is when she is at her most competitive, get that cover and peel out, rather than being exposed early which she has in some circumstances lately."

Imperatriz was exposed early in her defeat in the Newmarket Handicap (1200m) at Flemington on March 9 after which she was diagnosed with exercise-induced pulmonary haemorrhage.

Gleeson was not offering that as an excuse, saying statistics indicate that 90 per cent of horses have a small bleed when they run.

He said Imperatriz had quickly recovered from the Newmarket defeat and when placed under saddle the following Monday was back showing her normal traits, including having a buck.

Gleeson added that getting back to weight-for-age racing on Saturday was a huge advantage for Imperatriz who will meet the Newmarket winner Cylinder on 6kg better weight terms for a one-and-a-quarter length defeat.

He also pointed to Imperatriz's liking for The Valley where she can use the track confines to her advantage.

"I think it's that turn she likes as she's able to slingshot off it," Gleeson said.

"It was a surprise when she led in the Manikato, but the way she got around that corner, she's like a greyhound. She lowers, extends her stride.

"I think that's one big advantage for her in how much ground she can make up or extend away from the field."

Cylinder is the $4.20 second pick in early betting and will have to it from barrier one.

The James Cummings-trained three-year-old is also without a rider.

Ben Melham rode the colt in a gallop at Moonee Valley on Tuesday morning but has been booked to ride I Am Me ($13) with indications the Ciaron Maher-trained mare will kick off her campaign in Melbourne on Saturday.