The top echelon of three-year-old fillies await Don't Tell Mamma after her impressive victory at Caulfield.

Trainer Tony McEvoy was using the 1400m of Saturday's MRC Foundation Plate as a stepping stone for next month's 1600m fillies races.

However he was keeping his options open, having also paid-up for the daughter of Not A Single Doubt in the Blue Sapphire Stakes (1200m).

McEvoy wasn't sure whether the filly would handle a distance rise, but after her impressive victory confirmed plans for the Edward Manifold Stakes at Flemington on October 4.

Don't Doubt Mamma's victory saw her firm from $12 to $6 for the Group One Thousand Guineas at Caulfield on October 10, a race that McEvoy said was also in his plans.

Ridden by Luke Currie, Don't Doubt Mamma ($4) scored a half-length victory over the favourite Sacred Eye ($3.80) with Thames Court ($15) three quarters of a length away third.

"I thought this 1400m would tell us which path we should take and she seemed to lap it up," McEvoy said.

McEvoy said he had stumbled on a new riding pattern for the filly after a bad barrier draw at her last start at Moonee Valley.

He said the filly had previously been ridden forward in her races over 1000m in Adelaide.

"Matthew Nielson rode her first-up and said all she wanted to do was relax, so I took that on board," McEvoy said.

"So we told Luke to be patient from the bad barrier and told him to see what she can do.

"It was also a first-class ride by Luke today.

"It took Luke a while to get her balanced but when he did, she went from being some chance to being a dominant winner.

"Not many horses have that."