While his son Jason is established in the top 10 jockeys in Sydney, New Zealand trainer Richard Collett is keen to make his own mark with a satellite stable at Warwick Farm.

Father and son combined at Randwick on Saturday with Untamed Diamond who prevailed in a close finish to beat Sweet Serendipity in a 1200m-benchmark race.

Richard Collett has eight horses in work at Warwick Farm, hand picked as those he thinks are up to Sydney racing.

"Most of the horses we have here are stayers but this mare has been here for a year," Collett said.

"I wasn't sure she had won."

Untamed Diamond ($9) took until the final strides to get to the leder Sweet Serendipity ($26) and won by a nose in a finish that had Jason Collett wondering.

"Usually in a tight finish I sort of have some idea but today was a bit of a "wasn't too sure"," he said.

"Dad has won a few races here on a couple of Wednesdays but this is my biggest win for him with a horse from the Sydney stable.

"I'm really, really proud to see her get her nose in front on the line.

"I though it might be a bit heavy for her but, no, she managed to skip through it."

The Randwick track remained in the heavy range after the first two races with the morning dew keeping it there despite no rain for two days.