Sydney's autumn triple crown is at the mercy of star colt It's A Dundeel after he made a one-act affair of the Group One Rosehill Guineas on Saturday.

With the Randwick Guineas already in his keeping, It's A Dundeel was sent out at the prohibitive odds of $1.30 in the second leg of the triple crown over 2000m following the scratching of second favourite Fiveandahalfstar a day earlier.

It's A Dundeel settled near the back of the field before making a lightning run around his rivals coming to the home turn and had the race won from the top of the straight.

Jockey James McDonald had plenty of time to savour the win as the colt powered away to score by 6-3/4 lengths from Sacred Falls ($10) with Tatra ($13) a long head away third.

"He's exceptional. That's the best feeling I've ever had on a horse," McDonald said.

"Man, he's improved and I think as a four-year-old he's going to get better.

"That might sound silly but the way he's progressed this preparation, he's an unbelievable colt."

It's A Dundeel is an odds-on favourite to become the first horse since champion Octagonal in 1996 to complete the triple crown with victory in the Australian Derby at Randwick in two weeks.

New Zealand trainer Murray Baker has claimed his share of major Australian races with a top-class horses over the years but said It's A Dundeel deserved to be rated up with the best.

"He's right up there with The Phantom and Nom Du Jeu," Baker said.

The Phantom was a multiple Group One winner and placed in a Caulfield and Melbourne Cup while Nom De Jeu won the 2008 AJC Derby and was runner-up in that year's Caulfield Cup.

Baker wasn't surprised to see the colt dominate but admitted to a few nervous moments early in the race when the favourite was back in the ruck.

"It was a brilliant win," Baker said.

"When he was back second last I thought "geez", but we know he's got that big sprint and he can sustain it.

"The improvement he has shown from the spring to the autumn is amazing."

It's A Dundeel has won three Group One races and took his overall record to seven wins from 10 starts.

His biggest danger in the Derby appears to be Fiveandahalfstar, who missed the Rosehill Guineas to run in the $2.25 million Group One BMW (2400m) at weight-for-age next week.

"Of course the BMW is tempting but he won't go there," Baker said.

"The Derby is the race we want."