When Helene Happy Star contests Sunday's BMW Hong Kong Derby, trainer John Moore will actually be able to relax and enjoy the event for a change.

Normally mob-handed in Group Ones, Hong Kong's leading money trainer has just one runner to saddle up in the Derby for the first time since 2008.

Helene Happy Star - a Woo family affair that could see both parents and children Derby winners for a second time but this time together - was one of Moore's usual handful of hopefuls. Ultimately, Helene Happy Star is the only one in the field but Moore knows better than most that having numbers doesn't guarantee a trophy.

"The year that John Size won with Fay Fay, I think I had six of the 14 runners and I ran second, fourth, fifth and sixth but didn't win," Moore recalled this week. "I might only have one this time, but as long it's the right one, that's all I need. As long as Hugh Bowman can get Helene Happy Star to relax, he could be the right one."

Moore-trained Savvy Nature was the first reserve after getting the short straw in a ballot for the last place in the field, but others like Arpinati and Selkirk Star are deliberate absentees.

"When owners ask you to buy them a horse, they usually say 'buy me a Derby horse' because this is the race owners dream of winning," Moore said. "That's the magic of the race. But only one horse wins and sometimes you can do the wrong thing trying to get them into it."

A favourite Derby trivia fact is that Hong Kong's two Royal Ascot sprint winners, Cape Of Good Hope and Little Bridge, shared the experience of running last in the Derby - a race that they should probably never have started.

"Last season, we pushed Flagship Shine to run in it and tried to make him run 2,000m, something he was never meant to do," Moore admits, but is hopeful things are changing.

"We've taken a different route this time with Arpinati - when it became clear that even 1,600m stretches his stamina, I said to his owner, Mr Siu [Pak-kwan] that we should miss the Derby and let's just win races.

"Mr Siu said take whatever direction I thought was right and we won the Group Three with Arpinati last Sunday. The danger if you keep pushing for a Derby with the wrong horse is that you might never get them back."

Selkirk Star, who runs in a support race on Sunday, was different. The decision wasn't about distance, but whether to keep going towards the Derby or forget about it and give the horse minor surgery for a breathing issue.

"The right thing was to look after the health of the horse - he's got a decent future but gambling on getting him to the Derby could have risked that," Moore said.