A plan to target the Australian Cup with Humidor has paid off for connections of the gelding, which has chased down Caulfield Cup winner Jameka to win the $1.5 million feature at Flemington.

Trainer Darren Weir and stable clients bought a half-share in Humidor after the spring carnival and the former New Zealand-based horse transferred to Victoria's premier trainer.

Humidor had run on strongly in his three starts so far this campaign without quite winning but was up to the task in Saturday's Group One weight-for-age race on the big track at Flemington and out to 2000m.

After settling back, equal favourite Humidor ($4.20) was the widest runner into the straight and set out after the other favourite Jameka, which hit the lead early in the run home after racing close to the speed.

Jameka fought on gamely but Humidor overhauled her inside the final 50m to win by a long neck with 1-1/4 lengths to Exospheric third.

Weir said the Australian Cup had been the goal with the talented four-year-old.

"It's good when you get a good horse you can do it with," Weir said.

"He's shown good ability. The plan was when we purchased half of the horse was to aim at the Australian Cup and see how far we got.

"It's nice that it's come off.

"Each run has been good. He's just progressed nicely each run and we got a nice result today for everyone involved."

There was pre-race drama surrounding Humidor when it came to light stewards had found a plunger with a liquid substance in the horses feed bin during during a routine stable inspection at 3am on Saturday.

But chief steward Terry Bailey said there was nothing untoward about the incident.

The horse was supposed to get the substance Hemopar, a digestive aid, before his nightly feed on Friday but a stablehand had inadvertently left the plunger in his feed bin.

Bailey said giving the horse such a substance was not against the rules.

Weir said the Group One BMW (2400m) in Sydney in two weeks was the likely next target for Humidor.

Jameka is also heading to The BMW and trainer Ciaron Maher was proud of the mare's game performance for second.

"It was a super run. She ran a huge race," Maher said.

"She did a lot of work and then the pressure came on really early and she was probably entitled to be found wanting a bit late for the work she did. But she was outstanding."