Weir has been based at Ballarat for about 15 years but Just The Part's win in 2004 had been his only victory in a Ballarat Cup.
Aided by a rails-hugging ride by in-form John Allen, Kiwia ($8.50) got through at the top of the straight in Saturday's 2200m race to gave chase after 2016 winner Pilote D'Essai ($51) kicked away to a handy lead.
Kiwia reeled Pilote D'Essai in before drawing clear late to score by 1-3/4 lengths, with top weight Life Less Ordinary ($8) another 1-1/4 lengths away third.
“It's a big thrill,” Weir said.
“Every trainer wants to win their home town cup.
“It's great to be able to win it for a long-time client (Gerry Ryan) and with a good mate in Johnny (Allen).”
Despite Weir's concern about whether Kiwia, one of six runners for the trainer in the race, would show his best on a slow track, the five-year-old proved superior in claiming his first win in 13 months.
“The writing was on the wall last Saturday,” Weir said.
“Had he had a bit of luck he probably would have won that race last week.
“I wasn't sure about the slow track because he ran a bit ordinary at Flemington on Melbourne Cup day when they got the rain.
“But when he got up inside of Tradesman on the home corner I knew he was at least going to be in the money.”
Weir praised Allen who continued a spring carnival to remember having won a host of feature races in the past month including the Victoria Derby (Extra Brut) and Mackinnon Stakes (Trap For Fools) at Group One level.
The Irishman also won the Weir-trained Ringerdingding in the Group Two Sandown Guineas last Saturday.