Although the son of Redoubte's Choice from a Zabeel mare was at long odds in the 2500m Derby, Hayes had been confident he would run a big race.
"Even in trackwork he doesn't get going until he's gone over a long trip. I think 2500m is the minimum distance for him," he said. "It was a big run. He ran home with some great sectionals, which is always a nice guide."
The last 3-year-old to win the Sandown race was Count Ricardo in 2004. Since then, only two have contested the event, with Furio finishing eighth and Saddler's Story 11th in 2006.
Rawnaq will carry 50.5kg on Saturday and be ridden by Hayes' apprentice, Chad Schofield.
The former leading Sydney apprentice joined Hayes' team in August.
He had the option of going home but will stick with the Lindsay Park team.
"He will be doing the majority of my riding," Hayes said.
"He's a very promising young jockey and as my stable builds up I want to be building with him.
"It's going to be good timing for me and him."
Hayes plans to run Rawnaq second-up in the ATC Australian Derby at Randwick in the autumn.