Trainer Murray Baker always had an ace up his sleeve as he put a frustrating Melbourne spring behind him and steered his star colt It's A Dundeel toward Saturday's Australian Derby.

And when he played the card, it worked to such stunning effect that it turned It's A Dundeel into one of the shortest-priced Derby favourites in the history of the Randwick race and left his trainer reflecting on what might have been.

Baker added blinkers to his colt's raceday kit for last month's Randwick Guineas, the horse's second run this time in.

It's A Dundeel scored decisively in the Warwick Farm race and then won even more impressively in the Rosehill Guineas two weeks later, earning himself the prime position at $1.20 in Derby markets.

"In Melbourne he was getting too far back, even in the Derby down there he lost his chance by giving those other horses too much start," Baker said.

"But I always had the option of the blinkers.

"We knew he'd show more speed with them on because we'd tried him in them in New Zealand and always had them there as a tool."

It's A Dundeel had arrived in Melbourne last spring unbeaten in his first five starts, including the Spring Champion Stakes, only to finish second in the Mitchelton Wines Vase at Moonee Valley as a $1.30 favourite.

He went out favourite again in the VRC Derby and again got way out of his ground, running home strongly to finish seventh behind Fiveandahalfstar.

But Baker resisted using the blinkers on It's A Dundeel at that stage of his career due to a concern that they could make the colt race too keenly.

For the same reason, Baker had considered removing them for the 2400m of the Derby, but has adopted a policy of not altering a winning formula.

Victory in the Derby would give It's A Dundeel his fourth Group One trophy of the season, a feat that would place him among the elite.

If there is one concern it is the distance, but Baker is not a doubter.

"He ran on very well in the Derby in Melbourne, one of the best in the race," he said.

"He's stronger, bigger and better now. There's really no reason to think he won't run it out."

Baker isn't looking too far ahead for It's A Dundeel, but he hasn't ruled out a run against older horses in the Queen Elizabeth Stakes (2000m) on the final day of the Randwick carnival.