Williamson led the charge for the New Zealand contingent by producing blueblood trotters Liberty Stride and Ultimate Stride for emphatic victories.
Liberty Stride set the tone for a great night out for the Kiwi contingent when she powered away from her opposition to win the group 1 3yr-old fillies' final.
Williamson's renowned trotting skill shone through when the filly, who had galloped in two of her three Victorian starts, put in a faultless display to win by almost 20m for driver Anthony Butt.
"It is a big thrill for us - massive," Williamson said.
"We are just so thrilled to come here and win nice races; it is not easy. You do have to bring the right horses and if you have a nice horse this is what you can achieve."
Williamson had put the finals-night polish on the daughter of Muscle Hill and Jasmyns Gift at the Victorian stable of Brent Lilley and partner Tracey Cullen.
Williamson revealed his Victorian venture had become far more than just a business trip.
"I have been here for six weeks with him [Brent]. He has been a sensational host.
"His partner, Tracy, is up at 4.15am feeding the horses and their little son, Jack, has allowed me into their family. I have just had a fantastic stay."
Little more half an hour after Liberty Stride's demolition job, Williamson produced Ultimate Stride for an even more emphatic group 1 victory.
The son of Love You and millionaire mare One Over Kenny embarrassed his Australian opposition when he ran away with the 2yr-old trotting colts and geldings' final by nearly 40m.
Ultimate Stride powered through tough conditions as rain and wind pelted the Melton track during the group 1 event.
And although his Australian opposition could not match him, Butt revealed he could not get his charge to go any more slowly.
"The conditions weren't ideal. He was getting pretty keen that first lap. I couldn't get him going any slower.
"He just wanted to get on with it, but he was very good. He smashed them."
The New Zealand contingent added a third Breeders Crown title to the haul in dramatic circumstances when Kratos was crowned the 3yr-old trotting colts and geldings winner in the inquiry room.
The John and Joshua Dickie-trained squaregaiter was second past the post in a thrilling three-way finish with provisional winner All Cashed Up and third placegetter Majestuoso.
All Cashed Up galloped late in the run home, but it was not just a case of waiting for the horse to be automatically relegated, as he would have been under New Zealand rules, for breaking over the line.
An inquiry was held to decide whether All Cashed Up had either had not gained an advantage or at least was unable to maintain his momentum when galloping.
Stewards ruled All Cashed Up had not complied with Australia's breaking rules.
Star filly Princess Tiffany went down in a shock result in the 3yr-old pacing fillies' final.
Sitting parked throughout, and copping some minor interference before the home turn, took its toll on the Mark Purdon and Natalie Rasmussen trained 3yr-old when she was beaten into third behind upset winner No Win No Feed.
Princess Tiffany was caught late by fellow New Zealander Best Western, who continued her superbly consistent Breeders Crown campaign by finishing second.
The New Zealand pairing of Perfect Stride and Zeuss Bromac could not match brilliant Australian colt Be Happy Mach in the 2yr-old pacing colts and geldings' final but finished third and fourth respectively.
