The emergence of this year's Rosehill Guineas as an outstanding form reference through Cox Plate winner Ocean Park can be further underlined - albeit in less-celebrated circumstances - on Saturday.

Merlin Mustang, who arguably had the hardest run from a wide barrier in the Guineas before finishing midfield, will be one of leading chances in the Blacktown Workers Club Handicap (1500m) at Rosehill.

The Rosehill Guineas was won by the sidelined Laser Hawk from Ocean Park, the New Zealand star who is unbeaten in four Group One weight-for-age runs as a four-year-old.

But there is further merit in the form with horses finishing behind Ocean Park such as Silent Achiever (third) and Ambidexter (fourth) winning important spring races.

And Hoylonny's recent run of three Sydney restricted-class wins adds even more weight to the result.

Now it's now Merlin Mustang's turn, according to the trainer who made headlines a few seasons ago with the flying filly Chance Bye.

"No horse did more work than him in the Guineas and he probably shouldn't have even gone around in it," trainer Mick Tubman said.

"He had definitely had enough by then."

Merlin Mustang has raced twice since the Guineas for which he was trained by Michael Murphy, winning first-up on the Kensington track at Randwick before making the pace when placed at Randwick.

"They only got him late last time and tomorrow's race looks a little bit easier," Tubman said.

"Every time he races he gives everything he has got and you don't get many horses like that who are tough as boots.

"A lot of the time he runs under the radar but I think he'll be in there punching tomorrow."

Tubman says the key to Merlin Mustang's chances might hinge on how he travels to Rosehill from his Kembla Grange stable.

"He's a bastard on a float, he's a kicker," Tubman said.

"I think he is a bit claustrophobic but he doesn't sweat up or shake. He's just boisterous.

"If he gets to the races in one piece he never lets us down."

Providing Merlin Mustang runs to Tubman's expectations, the horse will return to the races within the space of seven days.

"The plan is to back him up in the Hawkesbury Cup on Thursday and then given him a freshen up before the Villiers Stakes," Tubman said."