Robert Smerdon already has the Blue Diamond Stakes favourite in his stable but he could have also have numbers on his side in the $1 million race.

Smerdon trains Fontiton, the filly who has been at the top of Blue Diamond charts since betting opened.

And now he has stablemate Thurlow heading the same way after she strengthened her claims for a Diamond start with a Group Three win at Sandown on Saturday.

In her first run since winning the Merson Cooper Stakes in November, Thurlow ($4.20) had blinkers on for the first time in the Chairman's Stakes and posted a half-length win over Haybah ($5.50) with the Gai Waterhouse-trained Brooklyn ($18) a short half-head away third.

Smerdon said he would discuss with jockey Craig Williams and representatives from owners Qatar Bloodstock before a final decision on whether she takes her place in the Blue Diamond in three weeks.

But he admitted a start was now likely.

"I would say they would probably want to go there," Smerdon said.

"It's an opportunity at a Group One race and she's a Group level winner now."

Smerdon has always insisted Fontiton, who is owned in different interests, has had a margin on Thurlow in everything they had done.

But Smerdon said the variables of racing can't be dismissed.

"Barriers, track conditions on the day and runs in the race. If you've got two bullets to fire it might be better shooting them both off," he said.

Thurlow is at $15 in Blue Diamond betting with Fontiton and the Mick Price-trained Secret Agenda, who are set to clash in the fillies Prelude next weekend, favourites at $4.60.

The Tony McEvoy-trained Stoker, meanwhile, has moved to $13 for the Blue Diamond after he sat close to the speed and then raced away to win the $250,000 Inglis Premier at Sandown on Saturday by 1-1/4 lengths.

His winning time of 56.28secs was 0.15secs quicker than Thurlow's winning time.

Thurlow settled fifth in the Chairman's Stakes with Parcel and Haybah on speed but the Smerdon-trained filly tracked into the race in the straight before sprinting to the front 200m out.

She tired late but lasted to again deny Haybah who finished a similar margin behind Fontiton last start but is not in Blue Diamond entries.

Maribyrnong Plate winner Prompt Return failed to fire after sitting third and finished fifth with jockey James Winks saying he was disappointing.