Gingernuts has made an immediate impression in Australia by becoming the fourth New Zealand-trained horse in seven years to win the Group One Rosehill Guineas.

The New Zealand Derby winner made his Australian debut in Saturday's 2000m race for three-year-olds at Rosehill and upstaged the locals in the heavy conditions to continue his rise.

Gingernuts ($6.50) defeated favourite Inference ($3) by 2-1/4 lengths, joining Jimmy Choux (2011), It's A Dundeel (2013) and Volkstok'n'barrell (2015) as recent New Zealand-trained winners of the race.

The Stephen Autridge and Jamie Richards-trained gelding needs to be a late entry for the Australian Derby but Richards confirmed the intention to run in the 2400m classic at Randwick in two weeks, with Gingernuts now $4.60 favourite.

"He's going to be awfully hard to beat in a couple of weeks' time," Richards said.

Richards felt Gingernuts had kept improving since the NZ Derby (2400m) and the drop in distance to 2000m on Saturday was countered by the testing conditions.

"It's a huge buzz. I'm really pleased for the team at home," Richards said.

"David (Ellis) bought the horse at the ready to run sales and didn't pay a lot for him and we syndicated him amongst some clients of ours and they're having a whirlwind ride."

Gingernuts carries the colours of Ellis' Te Akau Stud and Ellis is the managing owner of a syndicate which race the gelding.

Some of the 42 were trackside wearing specially made orange caps to match the horse's colours.

"We flew over for the day. We've actually got to leave in 45 minutes," said Craig Saunders, one of a handful of owners who made a flying visit from Auckland.

"Most of us are booked to come over for the Aussie Derby in a couple of weeks. It was a little spur of the moment to come over today but we thought we're on a hell of a ride and it doesn't happen very often."

Jockey Opie Bosson settled Gingernuts back before making his run around the field from the 800m.

Gingernuts reeled in leader Harper's Choice just inside the final 200m and despite tiring late, he had a comfortable margin over Inference on the line with So Si Bon ($20) another short half-head away third.

"He still wasn't 100 per cent happy in the ground but all the way up the straight he just had his ears pricked, looking around," Bosson said.

"He's a pretty good horse, and getting better.

"The way he's stepped up has just been incredible."