Just as it was in the Tulloch Stakes a week earlier, Quick Thinker has beaten Zebrowski to give champion New Zealand trainer Murray Baker his fifth Group One Australian Derby at Randwick.

Despite being in lockdown at home in New Zealand, Baker and also his co-trainer Andrew Forsman are still making an impact during this year's Sydney autumn carnival, with Quick Thinker turning in a determined performance to win Saturday's 2400m classic for three-year-olds.

With star New Zealand jockey Opie Bosson aboard, Quick Thinker was positioned just behind the pace and made his move around the home turn.

The Hawkes Racing-trained Zebrowski ($8) took an inside run and the pair staged a stirring duel in the straight, with Quick Thinker ($13) prevailing by a short head.

Queensland visitor Eric The Eel ($19) gave chase but couldn't peg them back, finishing another 1-1/4-lengths away third.

Baker has won more Group Ones in Australia than any other New Zealand-based trainer and Quick Thinker added to his Australian Derby haul having first won the race in 2008 with Nom Du Jeu.

Dundeel (2013) and Mongolian Khan (2015) added to Baker's Derby tally, while since being in partnership with Forsman he has won with Jon Snow (2017) and now Quick Thinker.

Quick Thinker is being housed at Baker's son Bjorn's Warwick Farm stables for his Sydney campaign and the colt emerged as a key Derby chance when he won the Group Two Tulloch Stakes last Saturday, beating Zebrowski by 1-1/4-lengths.

Baker said it was the plan to have Quick Thinker in a prominent position and said the three-year-old showed plenty of fight.

"Opie Bosson is a top class rider, his record proves that and I had complete faith in him," Baker said from New Zealand.

"He's quite a tough little customer. I thought he'd kick on a bit."

Bosson claimed his second Australian Derby after winning on Mongolian Khan.

"Murray Baker is a genius getting his horses ready for this race," Bosson said.

"He rang me yesterday morning and said the horse is rock hard fit and he'll run a huge race.

"To be honest, he pulled my arms out the whole race. He didn't come off the bit until we got to about the half mile.

"I thought we might have done too much in the running but then the Murray Baker fitness kicked in."

Bosson has based himself in Sydney for the autumn carnival and wins such as the Derby make the sacrifice of being away from his family in New Zealand a bit easier.

Baker admits he gave Quick Thinker a cheer from home but the veteran horseman says there will be no celebrations.

"We can't do much," he said.

"I'm just going to go and move my sheep. I've just got to move them on to better pasture."

Favourite Castelvecchio ($2.60) never threatened and dropped out in the straight to finish 21 lengths from the winner in ninth on a heavy track.

Trainer Richard Litt told stewards the colt did not love the wet ground and had been "knocked around a little bit", and was likely to go to the paddock.