Champion New Zealand trainer Murray Baker is in lockdown at home but as usual is making his presence felt on the Sydney autumn carnival.

The winner of more Australian Group One races than any other trainer based across the Tasman, Baker claimed his fifth win in the Group Two Tulloch Stakes at Rosehill.

Although Saturday's 2000m-race is just a week before the Australian Derby (2400m), the tough performance by Quick Thinker indicates he may be able to handle the back-up.

Several New Zealand horses were already in Sydney before coronavirus protocols were tightened last week and Baker and his training partner Andrew Forsman have Quick Thinker and The Chosen One.

Baker admitted he thought 2000m might be a query but watching from New Zealand he said Quick Thinker looked as if the 2400m of the Derby might not be beyond him.

"He is out of an Al Maher mare so I thought the distance might get him, but that was a good tough effort," Baker said.

"I was worried about the distance, not so much the (soft) track.

"He was pretty strong there, which is encouraging. "It is onto the Derby now.

"It is always nice to win and that is my fifth win in the race.

"I won it with Our Palliser (1987), The Bill (1993), Harris Tweed (2009) and Jon Snow (2017), so it has been a good race to me."

Jon Snow claimed the Tulloch/Derby double while Harris Tweed finished second to Roman Emperor in his year.

James McDonald, who rode the Baker-trained It's A Dundeel to win the 2013 Derby, rode Quick Thinker on Saturday but has committed to Castelvechcio in the Derby.

"I would love to keep McDonald because he rode Dundeel, but he is riding Castelvecchio," Baker said.

"There will be someone looking for a good ride like my bloke."

There is a pool of 25 jockeys who can ride in Sydney after the state was divided into regions to help minimise contact among riders.

While he will not be on Quick Thinker, McDonald believes he is a genuine Derby contender after the $2.70 favourite beat Zebrowski ($4) by 1-1/4 lengths with Diasonic ($13) another three-quarters of a length third.

"He is a proven wet tracker. He is fit and he'll be a force to be reckoned with come the Derby," he said.