New Zealand jockey Opie Bosson has claimed a big prize on Blue Sapphire Stakes day at Caulfield but is chasing an even bigger one at the same track in a few days.

Bosson won Wednesday's $150,000 Group Three Ladies' Day Vase (1600m) on the Danny O'Brien-trained mare Miss Rose De Lago, his only ride on the program.

On Saturday he partners favourite Mongolian Khan in the $3 million Caulfield Cup (2400m) and he believes the four-year-old dual Derby winner from last season is spot-on.

"He gives you a great feeling at the moment," Bosson said.

Bosson rode Miss Rose De Lago to a close fourth in the Group Two Let's Elope Stakes last month and was keen to stick with her.

"I got my manager to just keep ringing him and ringing him (O'Brien) so I could stay on," Bosson said.

O'Brien said he was pleased to have Bosson aboard and the mare led all the way for a convincing win.

The $3.40 favourite, Miss Rose De Lago kicked away turning for home and defeated Into The Mist by 3-1/4 lengths with Amarela a head away third.

She is now likely to have two Group One targets in her next two starts.

The former West Australian-based mare was transferred to O'Brien's stable earlier this year and she has won three of her seven starts since.

O'Brien said the Myer Classic (1600m) at Flemington and the Railway Stakes in Perth were on the radar.

"She came over from Perth. Owners Barry and Jan McRostie sent her across and we've kept her lightly raced over the spring to possibly go over for the Railway," O'Brien said.

"But the obvious race to run in before then is the Myer."