It's A Dundeel has become just the fifth horse to claim Sydney's three-year-old triple crown with the easiest of wins in the final leg, the Australian Derby.

By the time the Randwick Guineas and Rosehill Guineas are run, the 2400 metres of the famous Classic is not for the faint hearted.

In an awesome display on Saturday, It's A Dundeel jogged at the back of the field for the first part of the race before James McDonald took him to the outside on the turn.

He reached the front with ease and McDonald had him in cruise control as they went to the line six lengths ahead of Philippi.

It's A Dundeel went out the $1.24 favourite with Philippi second elect at $9.50 with Kingdoms defying his $101 quote to run third, 1-1/4 lengths behind the runner-up.

Trainer Murray Baker is used to winning big races both in Australia and his native New Zealand but says his latest star may be his best.

"He did it pretty easily, didn't he," Baker said.

"He's so relaxed and so laid back.

"To win three Group Ones in Sydney is pretty special."

In fact It's A Dundeel has won four Group Ones in Sydney with the Spring Champion Stakes in October his first.

That cemented him as the long-time Victoria Derby favourite but he couldn't manage a place, putting his ability to run the distance in question.

Those questions were answered emphatically on Saturday with Mick Kent, trainer of the runner-up, among the colt's admirers.

"My job was to come here and run second," Kent said.

"The winner is the best horse in Australia - as good as the mare (Black Caviar)."

Baker isn't prepared to put him that high yet but all going well It's A Dundeel will get the chance to prove himself against older horses in the weight-for-age Queen Elizabeth Stakes (2000m) in two weeks.

"We'll make a decision on that in the middle of next week," Baker said.

A new jockey will have to be found due to McDonald copping two suspensions out of last week's Golden Slipper day.

Top of the list is Hugh Bowman who rode the Baker-trained Lion Tamer to an equally devastating win in the 2010 Victoria Derby on a heavy track.

Although he will be missing for the rest of the Randwick carnival, McDonald has plenty to savour with It's A Dundeel.

"He was incredible," McDonald said.

"The race panned out perfectly. I couldn't believe the spot I was in.

"He is just awesome."

Kent will recommend a gelding operation for Philippi and John O'Shea will give the owners of Kingdoms the same advice.

"I think that qualifies him for the Caulfield Cup and I'll make the recommendation that he be gelded," he said.

"He ran well but the winner is a superstar."

It's A Dundeel joined other superstars of their classic years to complete the triple crown - Moorland (1943) Martello Towers (1959), Imagele (1973) and Octagonal (1996) - and is the equal favourite in most markets for the Cox Plate in the spring.