"I can't remember a day like this," New Zealand team manager Sue Walker, who has been attending World Championships since 2004, said.
For Williams it was a continuation of the consistent form she has shown since claiming world number two at the World Championships in Auckland in 2013.
Despite not getting a good start and being only sixth to the first corner, she picked her way through the field and finished with a strong last straight to claim third.
James also had a mediocre start and was last into the first corner but her fitness saw her come through the field and overtake two riders on the final straight to collect her second world ranking of the meeting after finishing fifth in her Cruiser class on Tuesday.
In her fifth attempt at the World Championships, Hawke's Bay's Amy Martin made a final for the first time and held third until the final corner when two riders dived inside her, shuffling her back to fifth. Her previous best result had been making the semifinals.
Leila Walker started her final as the five-time defending champion and on the back of an unbeaten day of racing through three qualifying motos, an eighth final, quarter-final and semifinal.
She raced neck and neck with Dutch rider Lissi van Schijndel down the first straight. Van Schijndel held Walker wide through the corner and the pair touched as they hurtled into the first jump on the second straight.
It was enough to unbalance Walker, who lost momentum and control of her bike and crashed. Van Schijndel easily won the race as she and Walker were a class above the rest of the field.
There were any number of hard luck stories, with Te Awamutu's Cooper Merito the only male to reach the semifinals where he crashed in the first corner.
Rico Bearman, who won the 15-16 Cruiser on Tuesday, was involved in a three-rider accident in the eighth finals, but had looked good to progress a lot further.
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