An impressive victory by Runson at Caulfield has turned into a triple treat for apprentice Liam Riordan.

Apprenticed to Leon and Troy Corstens at Flemington, the victory on Runson in the Bill Collins Handicap was Riordan's first Saturday metropolitan success.

Runson's win also provided Riordan with his first metropolitan winner for the father-and-son training partnership along with the end of his apprentice claim on provincial and country tracks.

Riordon's claim of 3kg brought Runson's weight down to 59kg on Saturday and after booting forward he was able to control the race.

Kicking clear on straightening, Runson ($9) scored by four lengths from Chippenham ($6) with the $4.80 favourite Catesby a long neck away third.

Riordan, 20, has ridden 85 winners and is in the second year of his apprenticeship.

"I've been with Troy now for four years," Riordan said.

"I've had a few indiscretions along the way and without Troy I wouldn't have a job."

Runson has become a bit of a favourite for Riordan, who has ridden the gelding on four occasions, for three wins.

"He used to be a sprinter, breaking track records, but he's now settling a lot better," Riordan said.

Troy Corstens credited former jockey Eddie Cassar with getting Runson to settle, firstly in his trackwork and more lately in his races.

"Eddie's been with the stable now for about six months and he's done a lot of work with this horse," Corstens said.

"He said that the horse would one day get 1400 metres, which I doubted, but he's been proven correct."