After dominating an 1100m maiden at Bendigo from the front on debut last month, Moldova raced in a prominent position throughout in Saturday's Jack Styring Plate over the same distance on the Flemington straight course.
With Prebble aboard, the Danny O'Brien-trained Moldova, the $3.30 favourite, was able to edge away over the final 400m and beat the closing Knowles ($41) by three quarters of a length with the same margin to La Lucciola ($9) third.
Prebble said Moldova was still raw with plenty of improvement to come.
“She's a big strong filly with plenty of scope about her,” Prebble said.
“She's got plenty of upside. She doesn't know what she's doing and she's still winning.
“If she gets a bend and a rail to follow you will probably see a better horse.
“It was her first time racing down the straight today, down the middle with no rail to follow. I thought it was pretty impressive.
“I'm not sure how high she will go but she's just got lots of upside.”
O'Brien's racing manager Matt Harrington said they would see how Moldova comes through Saturday's race before determining immediate plans.
“She's done a good job in her first preparation,” Harrington said.
“The key is going to be how she pulls up and then we'll make a decision what we do next.
“We'd love to go to a stakes race at some stage. Whether that's as a three-year-old or now, that's what we'll have to work out.”