Military Attack's jockey Zac Purton went behind enemy lines yesterday to ride rival runner Criterion, a horse whose co-trainer David Hayes says returns in much better shape than on his first trip to Sha Tin, reports the HK Racing Post.

Criterion had been under Hayes' care for little more than a month when third behind Designs On Rome in last year's Hong Kong Cup, a run that came at the end of a long preparation for the four-year-old and included complications in the final weeks before the race.

This time Criterion arrives off a dominant victory in the A$4 million (HK$24 million) Queen Elizabeth Stakes in Sydney and Sunday's tilt at the HK$20 million Audemars Piguet QE II Cup will be just the fourth run of a preparation that could culminate with a shot at the Prince Of Wales's Stakes at Royal Ascot in June.

Hayes was trackside yesterday and joked with an adoring local press that having Purton aboard in the absence of regular rider Craig Williams, who arrives on raceday, was "like sleeping with the enemy".

"I know Zac is very good with his times and I didn't want the horse to do too much," Hayes said. "I was very happy with the way he rode the horse."

While Caspar Fownes-trained Military Attack worked with a riding boy aboard, later in the morning Purton set off from the 1,200m at a steady tempo on Criterion before sprinting home the final two furlongs comfortably in 24.2 seconds.

"He wasn't out there to do anything too drastic," Purton said. "I just let him quicken up in the straight, he is a very relaxed horse, very professional and he did everything right. He gave me a very good feel and I think he is going to be very hard to beat on the weekend."

Hayes, a two-time Hong Kong trainers' champion who now works in partnership with his nephew Tom Dabernig, has the benefit of some familiarity with Criterion on the horse's second trip to Sha Tin - where the chestnut will start among the favourites after being sent out a 38-1 outsider on international day.

"I know him now, I was guessing last time and I know what to do with him because I've been training him for six months," Hayes said. "Last time he had a far from an ideal lead-up to the race.

"We thought he had colic just before we took off, but it was actually an allergy to a tick medication. So he was treated for colic when he didn't have it, which is not great eight days from a race.

"Then the rash was so bad that we couldn't put a saddle on his back. He missed five days of his 12 leading into the race and yet he still ran well.

"It was also his seventh run in. He had backed up from a Cox Plate to a Mackinnon Stakes in seven days, and this time he comes in fourth-up and his races have been spaced."

Criterion faces a 15-day turnaround this time, but if he comes through Sunday unscathed, then a trip to Royal Ascot beckons.

"That quick backup is my only concern, I would prefer three weeks between runs when travelling, but it doesn't look like it has worried him," he said.