Dropping back to 1100m after a Flemington win over 1200m on June 7, Marble Nine ($8) scored a 1-½ lengths win from the $2 favourite Cleo Cat with Midwest ($13) in third place.
Troy Corstens said it would be hard to take Riordan off Marble Nine after Saturday's win.
"Liam is one of the hardest working kids out there," Corstens said.
"He was apprenticed to us and I've got a real soft spot for him. He doesn't get a lot of opportunities, but he's going really well at the moment.
"It's nice to give him a birthday present for yesterday and you wouldn't take him off now, but in fairness, Hannah (Edgley) would have stayed on had it been a claiming race.
"She had done nothing wrong, but it wasn't and it's hard to justify putting a claimer on."
The Corstens team won the corresponding race four years ago with The Astrologist with that horse going on to claim the corresponding Stakes race two weeks later.
Corstens said the stable was a little concerned with the drop back in trip.
"We were a little worried about dropping him back to 1100 metres thinking the 1200 might be better for him," Corstens said.
