In-form jockey Zac Purton will ride Ambitious Dragon when the two-time reigning Horse of the Year returns later this month, giving the Australian first crack at securing the much sought-after ride in the upcoming features.

Purton will become the third jockey in as many starts to ride the Tony Millard-trained horse, after Douglas Whyte and Umberto Rispoli filled the hot seat in his last two runs - both losses at Group One level.

It is understood that Rispoli, who is riding in France, could not commit to the Group Two Oriental Watch Trophy in three weeks, gifting Purton his first ride on the six-year-old, and his first ride for Millard in nearly two years.

"It's a real honour and a privilege to ride such a good horse - he is obviously the best horse we have here in Hong Kong at the moment and I'm very grateful to be given the opportunity," Purton said.

"At this stage it is just a race-by-race booking, from there, the owner, Mr [Johnson] Lam, and Tony can assess how I gel with the horse and decide what they are going to do after that, I know Umberto Rispoli is coming back - I can't pretend that I've secured the ride for good, but it's a start and hopefully it works out well."

Millard said the six-year-old will trial around a week out from his first-up start, before heading to either the Jockey Club Mile or Cup on November 18, and then on to a career-defining contest on Longines International Day (December 9).

Purton's strong recent form - he finished second in last season's Jockeys' Championship and rode a double yesterday to take him to 10 wins and extend his early season lead - secured him the mount.

"That was the most important factor, that we got a jockey who is riding well," Millard said. "We'll see if he is suited to the horse and go from there."

Purton, 29, has increased his win total in each of his five seasons riding in Hong Kong but has had limited opportunities on genuine Group One horses.

"It's so hard to get into these top horses here in Hong Kong, it's a great opportunity and hopefully I can make the most of it," he said. "Little Bridge and Fellowship have basically been the only two horses I've ridden at the top level since I've been here, and I've done a good job on them in the big races, so it's a chance to build on that."