She stretched out in the slow ground to hold Sidestep ($11) at bay by 1 lengths, with a length to Sweet Idea ($10).
Doubts about her ability in wet ground made punters a little nervous about Overreach with as much as $3.10 bet before she was wound in to $2.80 after being $2.30 early in the week.
She covered the 1200m in 1:11.
"She showed her superiority," Waterhouse said. "I'm so admiring of Tommy Berry. Not only is he a capable jockey, he has the ability to be able to flow with things."
Berry told Waterhouse he wanted to stick to the fence and she gave him carte blanche to do what he thought best with one proviso.
"You do what you like as long as you win," she told him.
Craig Williams, rider of Cambridge filly Ruud Awakening who beat one home, said: "We ended up not flying the start so we used plan B and went back. We followed Villa Verde into the run but just never travelled like I thought she was going to."
-AAP