The Group 1 Empire Rose Stakes (1600m) at Flemington on Victoria Derby Day, a race restricted to fillies and mares, is likely to be Grinzinger Belle's ultimate goal for the campaign.
Taken to the front by Damian Lane, Grinzinger Belle ($21) scored by four lengths from See You In Heaven ($6) with $5 favourite Alsephina a half-neck away third.
Grinzinger Belle has an affinity with the 1400m journey at Flemington having won the Group 3 The Vanity when resuming in February.
"She won The Vanity in the autumn first-up and we thought she was in similar order today, but tackling a deeper field," O'Brien said.
"There were some very classy mares in that race today. She always travelled well in the run, but I didn't think she'd open up and win like that.
"We're really pleased that she's come back as well as she did.
"She's a good Kiwi-bred who is by Shamexpress, who we trained, and is close to our hearts and she seemed to really appreciate those conditions."
O'Brien said Grinzinger Belle could head to Moonee Valley on Grand Final Eve for the Stocks Stakes (1600m) or return to Flemington for the Group 2 Rose Of Kingston Stakes (1600m) on October 5.
"She really cuts out at the mile, but I think we'd aim to be here on Derby Day for the mares' Group 1," O'Brien said.
As the field paraded for Saturday's race and made their way around to the start, a shower of hail descended on Flemington.
Lane said the appalling weather did not seem to affect Grinzinger Belle.
"It seems as though she's been in the paddock with plenty of weather because she wanted to face towards it, so I had to explain to her that you're better off facing your bum to the hail," Lane said.
"Once she figured that out, she handled it quite well.
"She huddled up with a couple of others and it obviously didn't affect her performance."
