Waterhouse has won a record-equalling six Golden Slippers to go with seven Sires' Produce Stakes in Sydney and five Champagne Stakes.
“She drew the outside in the Prelude so I had to do a bit of work to get across and I thought she held on really well,” Baster said.
“She had improved with every bit of work she had done and she worked really well at The Valley last Saturday.”
Vinicunca has drawn barrier four in the field of 14 and is expected to take up a prominent position again.
“Obviously Gai's horses are best when they are rolling along but we'll just play it by ear,” Baster said.
Vinicunca was $21 after Tuesday's barrier draw but has tightened to $10 with Lyre, who beat Vinicunca in the Prelude, the $6 favourite on race eve.
Athiri, third in the fillies Prelude, is also among the main chances at $8.