Josh Parr's decision to ride Shadow Hero in the Spring Champion Stakes at Randwick has been vindicated with the promising stayer scoring a hard-fought Group One win.

The jockey had to make a touch choice between Shadow Hero and Castelvecchio, who he also rides regularly and won a Group One race aboard in the autumn.

Parr admitted the pressure of the decision took its toll in the lead-up to Saturday's race and he was flooded with a mix of joy and relief when the Mark Newnham-trained horse got the job done.

"I'm really emotional right now," Parr said.

It has been a build up of pressure and so much has been spoken of the battle of the two horses and whether I'd made the right decision. I'm really proud."

I was confident when I first let him down then it was a bit of a battle to reach the first two but when he got alongside them it was all over, he was determined to win."

Solid in the market at $1.90, Shadow Hero had to dig deep when race leader Just Thinkin' ($8) and eventual third placegetter Battenburg ($41) kicked at the top of the straight.

He set sail for the frontrunners, as did runner-up Castelvecchio ($3.10) but Shadow Hero held his assailant at bay by a length with another half-head to Battenburg.

The victory cemented Shadow Hero's place at the top of Victoria Derby markets and gave Parr his second win in the race after Hampton Court five years ago, while Newnham landed back-to-back Spring Champions, taking it out with filly Maid Of Heaven 12 months ago.

Newnham said he had some anxious moments as the field turned for home but had equal faith in his horse's stamina.

"I was just hoping that the real strength he's shown in all his races would kick in," Newnham said.

"The other day everything went right for him and today it has been hard to make up ground but his superior staying qualities kicked in.

It is just nice a plan has come together and it's come off."

Brenton Avdulla said the Richard Litt-trained Castelvecchi did a good job to grab second after stepping up sharply in distance from the Golden Rose.

"'He's just missed out today. He is a talented colt," Avdulla said.

The surprise of the race was maiden Battenburg who briefly hit the front at the 200 metres and was game in defeat.

"He has run a huge race. For a maidener having just his fourth start, I couldn't have asked for any more of him," jockey Rachel King said.