David Eustace’s satisfaction from seeing Charity Gain deliver on expectation quickly turned to surprise when Young Emperor saluted at knockout odds to complete the handler’s maiden Hong Kong double at Happy Valley on Sunday.

Eustace only saddled up three runners at the city circuit’s annual day fixture but that didn’t stop him landing a 240-1 double to take his win tally to three in his first season training in the city.

A horse Eustace identified before the season as one with ability, Young Emperor was disregarded by punters after failing to set the world alight at the trials ahead of his Hong Kong debut.

“I’ll be honest, it took me by surprise. I hoped he would just run well,” said Eustace, who jetted back to Hong Kong for Sunday’s meeting after watching his brother Harry’s horse, Docklands, run fifth in Saturday’s Group One Cox Plate (2,040m) in Melbourne.

“Having said that, his best trial was actually here at the Valley. I thought he was a touch underwhelming in his trials prior to that but I always quite liked him.

“He’s a really good-looking horse and he’s by the right sire. He got a great ride from Luke [Ferraris] and he finished off well.

“I’ve been away for a couple of days and [assistant trainer] Cash [Lee Tsz-wai] and the team have done a great job. I think I need to go away more often.”

A winner of one of three pre-import starts in Ireland, $42.8 chance Young Emperor settled behind midfield in the Class Three Zhaoqing Handicap (1,200m) before powering down the middle of the track in the home straight to grab $2.5 favourite Romantic Son, who was also making his Hong Kong debut.

“He was three-wide but he had cover the whole way. I actually like that,” said Eustace.

“I think it gives horses and jockeys room to manoeuvre when they want. I think it’s probably the ideal place to be if you’re not up in the first three.”

Eustace was pleased to deliver with his first runner for the Racing Club – the Jockey Club’s young members arm – and didn’t rule out a Classic Mile tilt with a galloper who will now be rated in the mid-70s.

“It was great to get that for [the Racing Club] and he’s a nice horse,” said the trainer.

“To me he looks like an out-and-out seven-furlong horse, but he relaxes and he got through the line well. I wouldn’t necessarily be in a rush to get to a mile but [the Classic Mile] could be a target.”

After a vastly improved second in his first run for Eustace on October 9, Charity Gain was sent off a $5.65 third favourite for the Class Four Shenzhen Handicap (1,800m) and he also barrelled home down the middle of the Happy Valley straight after travelling behind midfield.

“We were quite confident coming into today that he’d improve a lot,” said Eustace.

“It was great to see him win. He put the writing on the wall last start and I think he’s a horse that will improve a lot.

“You always worry a bit coming to Happy Valley that you need to get the right run but Vincent [Ho Chak-yiu] rode him with confidence.”

Eustace paid tribute to prominent Australian owner Colin McKenna, who died on Sunday after a short battle with illness.

“I must just say it’s been a difficult day for Australian racing. Ciaron Maher’s major owner, Colin McKenna, passed away this morning,” said Eustace, who trained in partnership with Maher before moving to Hong Kong.

“He was a great supporter of [Ciaron] and Australian racing across the board. We’re thinking of Janice, his wife, and their whole family.”

Ferraris and Ho were both completing doubles when saluting for Eustace, with the former also victorious aboard Smart Fighter for Ricky Yiu Poon-fai and the latter beginning his brace by triumphing atop the Manfred Man Ka-leung-trained Sturdy Ruby.