Watching a horse he sold go on to win a Group One in Melbourne on Saturday brought mixed emotions for Te Aroha trainer Peter Lock.

On one hand he was delighted for Sierra Sue's trainers Trent Busuttin and Natalie Young when she was victorious in the Group 1 Sir Rupert Clarke Stakes (1400m) at Caulfield, and on the other he was ruing what might have been had she stayed in his care.

But a philosophical Lock admitted it is the business of racing, and trading horses is a major component of running a viable stable.

“The biggest disappointment is having to sell a horse like that to survive, but such is life, you have just got to move on and hopefully find another one,” Lock said.

While he is no longer in the ownership group, Lock said he and his family are getting a great thrill out of following Sierra Sue's success in Australia, which also includes victory in the Group 2 Rose of Kingston Stakes (1400m) and Group 2 PB Lawrence Stakes (1400m).

“We are getting a great thrill out of it,” Lock said. “Casey, my daughter, and Jamie, my son, we are on the phone all the time and they come to my house to watch her races. It is like we own her.

“Trent Busuttin is a very good friend of mine and we are on the phone quite a bit. I couldn't be happier for the owners.”

Lock first laid eyes on Sierra Sue at New Zealand Bloodstock's Karaka sales complex at the 2019 May Sale.

While wary of buying a broken-in two-year-old, Lock liked what he saw and elected to take a punt on his hunch and secured the Darci Brahma filly out of Ardsley Stud's draft with a bid of NZD$2,000.

“I saw her at Karaka and I love Darci Brahmas,” Lock said. “I walked her up and down and I was just a bit concerned that she was two-years-old and broken in.

“She was a massive, big scopey filly, and I thought she was never going to make a two-year-old so I took a punt on her.”

Lock was delighted with her progress at his Te Aroha barn and first saw glimpses of her potential at the Cambridge trials just four months after her purchase.

“Everything we did with her she just improved,” he said. “In her first trial she ran fourth at Cambridge and she went huge but she was a bit shin-sore, so I turned her out for eight weeks.

“I trialled her at our local meeting at Te Aroha over 1000m and she absolutely donkey-licked them by about six lengths and I knew then that she was a very good horse.”

Lock wasn't the only one impressed by her trial, with Cambridge-based bloodstock agent Phill Cataldo also taken by her efforts.

“I mentioned to Phill Cataldo, who was there, that she was the nicest horse I had had in a long time. A week later he came back and said he had some clients who wanted to buy her,” Lock said.

She was subsequently sold to clients of Busuttin Racing, which includes well-known owner Ozzie Kheir, and she has gone on to win eight of her 18 starts and more than AUD$1.1 million in stakes.

Meanwhile, closer to home, Lock is looking forward to continuing Group One performer Hiflyer's spring preparation at Matamata this weekend.

The nine-year-old gelding had his first start in more than two years when tackling New Zealand's best in the Group 2 Foxbridge Plate (1200m) at Te Rapa last month.

Despite failing to beat a runner home, Lock was pleased with Hiflyer's first-up run, particularly against a high-class field after his extended hiatus from the track.

“We were over the moon with his run in the Foxbridge. It was his first go for more than two years and he has improved a tonne,” Lock said.

“Everyone said ‘why did you go there', but if I had have gone to an Open 1200m I would have got 65 kilos and he would have tailed off even further. If he hadn't got interfered with at the start he would have been a lot closer than he was.

“He deserved his place in the line-up and once he gets a few more runs under his belt you will see the real Hiflyer.”

Lock has taken a cautious approach with Hiflyer's return and has withdrawn the gelding from the Group 1 Windsor Park Plate (1600m) at Hastings on October 2 in favour of some softer options.

“I was a wee bit hasty in pulling him out of the second day at Hastings but just to be fair on the horse I didn't want to put him under any pressure,” he said.

“He will run in an Open 1400 at Matamata on Saturday and I think people will see a hell of an improvement on that run.”

Group One aspirations remain high in the agenda for Lock, with summer targets particularly in the crosshairs.

“The Thorndon Mile (Group 1, 1600m) is my main target with him,” Lock said.

“Trentham is a lovely, big roomy track and you have got time to get back and get over them if you are good enough.

“He deserves a Group One this horse.”