The stable won the $45,000 listed New Zealand Bloodstock Insurance Stakes for 3yr-old fillies at Wingatui on Saturday with No Choice.
The stable won the Canterbury Belle Stakes, the first race in the Southern Filly of the Year series, with Princess Emmy.
The two fillies share the lead in the four-race series.
The Riccarton stable has contributed 16 wins for Sargent's tally of 50 this season.
Carston was instrumental in the lease of No Choice in December after the filly had recorded a fourth from three starts from the Cambridge stable of Murray and Bjorn Baker.
He was offered the filly by Christchurch agent Roddy Fulton on behalf of Singapore breeder Akthar Mann.
Carston now races No Choice with Gerard Brown and Lance Mitchell of Christchurch and Graeme Laing and Tim Rodger of Matamata.
"I liked her because she was by Coats Choice," Carston said.
Coats Choice is making his mark with his oldest progeny 3yr-olds.
The son of Redoute's Choice is also the sire of Milo (Dunedin and Gore Guineas) and Five Coats, who ran third to No Choice on Saturday. No Choice is the seventh foal of Winkum, an unraced mare by Waikiki Star.
No Choice came from the rear of the 16-horse field at the 400m to win by a length and a-half over the 1400m in the hands of Jamie Bullard.
• Smudgee is proving a Wingatui specialist with her fourth win on the track on Saturday. The 5yr-old mare was among four winners on Saturday for the North Taieri stable of Brian and Shane Anderton.
Smudgee (Yamanin Vital-Renee) was bred by Brian and Lorraine Anderton who sold her out of the paddock as a yearling to Gordon Dickson, of Invercargill, and Maurice Hampton, of Wyndham.
Smudgee is the sixth foal of Renee, winner of the 1995 Stewards' Handicap at Riccarton when trained by the Andertons.
Renee is also the dam of Renee Maree (four wins).
The Anderton stable also won on Saturday with Royal Flight, Beata and Jaylay.
Royal Flight, who had not raced four months, is headed to the South Island Breeders' Stakes at Riccarton on March 26.
The stable also has Inferno aiming at that race.
Jaylay is a Yamanin Vital-Ebony Bijou 3yr-old filly raced by Brian and Lorraine Anderton.
• Courtney Van Der Werf stood down from her last three engagements on Saturday after she injured her shoulder.
She was feeling the effects of a fall when she rode Wine'nsoda (race 4).
"She will have physiotherapy and should be clear to ride on Thursday," Michael Pitman, her employer, said.
Shamrox, the beaten favourite in the open sprint, had difficulty breathing during the race, rider Daniel Stackhouse told stewards.
Trainer Kezia Murphy said that Shamrox would undergo surgery for a soft palate.
St Bernard bled during race 6, incurring a mandatory three-month stand-down from racing.
