Golden Slipper placegetter Mamaragan has earned his chance at the Group One Sires' Produce Stakes, a race his trainer originally dismissed as an option.

John Thompson had him pegged as as a pure sprinter and early on was eyeing a Magic Millions campaign.

Mamaragan's debut was delayed by shin soreness and he burst onto the scene in one of the key Golden Slipper lead-ups, winning the Group Two Skyline Stakes at Randwick on February 29.

Three weeks later he finished third behind more seasoned juveniles Farnan and Magic Millions winner Away Game in the $3.5 million Golden Slipper at Rosehill.

His owners have paid a late entry fee to give Mamaragan his chance over 1400 metres in Saturday's Sires' (1400m) and he headlines a field of 15 with Nash Rawiller retaining the ride.

"Personally, I thought he was a speed horse," Thompson said.

"They were my early thoughts and that's why I didn't nominate him for the Sires'.

"But from day one when Nash has got on him he said he'll make a nice 1400-metre, mile horse.

"That's the feel the colt has given him.

"He relaxes nicely in his races and he's got a high cruising speed. I've got no hesitations at all about 1400.

Mamaragan was the $4.40 favourite on Tuesday after drawing barrier two and Thompson said it was all systems go for Saturday.

"It wasn't ideal that we went into the Slipper at his second start but we had to play the cards we were dealt and to the horse's credit he performed very well," Thompson said.

"It was a little bit of a shame he was a bit slow to jump. He had barrier one and he was in there a while and just stepped away a bit slow when he probably would have been up on the speed.

"He's drawn well again on Saturday and he seems to have come on again from the run.

"The best lead-up form for the Sires' is always the Slipper and he's probably the horse that's come out of that that's done the best.

"So you'd probably say on form he's the one to beat."

Thompson said Mamaragan had always shown talent but the Randwick trainer is convinced the colt will only get better next season.

"Whatever he's doing now he's just doing on natural talent," he said.