Casey, of Winton, rode Bellarook to win the 1961 Stewards' Handicap.
He was then employed by Ted Winsloe, the Gore trainer of Bellarook.
It was the third time Casey had campaigned a horse at Riccarton as a trainer and his first win on that track.
South Gate was recording her second win.
The 6yr-old Justice Prevails-Night Alert mare won a maiden race at Gore in October.
Night Alert is by Trustful from Cottage Gate, a half-sister by Gate Keeper to Middy, winner of the 1969 New Zealand Cup.
"I was training her for the Winton Jockey Club on lease from Tom White [the breeder] and they didn't want to carry on so I took her over this season.
I felt she was capable of winning a couple of races," Casey said.
His other horse, Fiddler's Green, has returned to work.
Fiddler's Green won a maiden race at Gore in December.
John Phillips, another Winton trainer, won with Doeface on Saturday.
Casey and Phillips are among about six thoroughbred trainers at Winton.
Trainer Michael Pitman was represented by four winners at Riccarton on Saturday - Le Thunder, Our Genes, Sand Toyz and Balzane.
He took his tally for the season to 65 wins.
He is third on the National premiership behind Mark Walker (100 wins) and Murray and Bjorn Baker (68). Le Thunder gave Pitman his third win in the Amberley Cup.
He won the race with Peyow Peyow last year and Honour Bright in 1990.
"The plan is for Le Thunder to race in the Whyte Handicap at Trentham next month. Kenny Starfighter, who was unlucky when he ran third on Saturday, may also race there," Pitman said.
Le Thunder and Our Genes have been nominated for $100,000 Winter Cup at Riccarton on August 1.
Our Genes and Sand Toyz were ridden by David Walsh, who walked the Riccarton track on Saturday morning and decided that next to the inside rail was the best footing in the heavy ground.
Pitman returned from Brisbane last week after deciding not to carry on the campaign of Borninthestates.
"He is not quite right and will come home and go for a spell," Pitman said.
