Imported stayer Big Duke has given premier Victorian trainer Darren Weir his first Sydney winner, but had to do it via the stewards' room.

Big Duke ($4) and Our Century ($3.10) fought out a two-horse battle down the heavy Rosehill straight in Saturday's Group Three Manion Cup (2400m) with Our Century a nose in front of Big Duke on the line, with 12-1/2 lengths back to Allergic.

Big Duke's jockey Craig Williams, however, quickly lodged a successful protest alleging Our Century shifted out to take his line of running and made contact three times over the final 300m which cost him more than the nose margin.

Chief steward Marc Van Gestel said Ben Melham shifted out and made contact with Big Duke inside the final 300m and also took Big Duke off his line by two horses.

He also said late in the race Williams was restricted in his ability to ride Big Duke out to the finishing line, so stewards upheld the protest.

Weir has been a dominant force in Victorian racing in recent seasons and set a new Australian record for most winners in a season in 2015/16 with 348.

He is on track to break that this season but a Sydney win had eluded him.

"It's obviously been the monkey on the back," said Weir's Warrnambool stable foreman Jarrod McLean, who was representing the stable at Rosehill.

"We've talked about it but there's never been any pressure.

"It's not as if we've been coming up here for the lesser races. We've had runners in the Epsom, the Doncaster and races like that and they're hard enough to win at any stage. But this is a good race to win."

Big Duke won the Launceston Cup at his previous start and McLean said the Chairman's Stakes in two weeks and then the Sydney Cup is the plan with the stayer.