The nature of Shadow Hero's Gloaming Stakes win sealed the deal for Josh Parr as he grappled with the decision of which horse to ride in the Spring Champion Stakes.

Parr is the regular partner of Shadow Hero and Champagne Stakes winner Castelvecchio but with the pair to clash in Saturday's Group One Randwick showpiece, Parr had to make a tough call.

"People say it's a good position to be in when you've got choices, which is definitely correct," Parr said.

"But I wish I was riding them both in different races.

"I try to be as loyal as possible wherever I can and I've won a Group One on Castelvecchio, so there is that emotional attachment to him.

"But when Shadow Hero was so dominant in the Gloaming, that was when the decision was made."

Betting operators reckon Parr has made the right move, marking Shadow Hero odds-on favourite on Friday, ahead of Castelvecchio with New Zealand raider Quick Thinker and Tulloch Lodge's Just Thinkin' the only other horses regarded as serious threats.

Shadow Hero showed a brilliant turn of foot to overwhelm his rivals in the Gloaming Stakes (1800m) and that race has traditionally been the best form reference for the 2000 metres of the Spring Champion.

Parr says it is that acceleration and the horse's ability to conserve energy that sets Shadow Hero apart.

"It is a massive advantage for a horse that can show that turn of foot over those distances," Parr said.

"Where this horse is exciting is he has a stride that covers a lot of ground. He does it quite easily and he doesn't use any unnecessary energy.

"He is an exciting prospect as a stayer."

The one query is whether Shadow Hero can handle a wet track.

Randwick was in the good range on Friday morning but with showers forecast, conditions could change quickly.

Shadow Hero's five starts have all been on firm ground and Parr admits a rain-affected surface will add an unknown element.

"Breeding suggests he is going to be OK on it and one thing you do need on wet tracks is a fit horse and that's the case with Shadow Hero, he is very fit," Parr said.

"We will just have to wait and see and have confidence in the horse."

Shadow Hero is the linchpin in an outstanding book of rides for Parr at Randwick.

He has seven mounts and all of them are single-figure odds, two of them favourites including Bottega in the Group Two Stan Fox Stakes (1500m).

"I'm excited to get there," Parr said.

"Johnny Walter has done a good job, my manager, he's secured some very nice horses there on Saturday from my first ride to my last ride."