Henshaw landed two "clean" consecutive 1080 degree double cork tricks during the second of his slopestyle runs - a move never seen before in competition, Freeski Open judge Dion Newport said.
The two tricks, effectively a double rotation and combined somersault through the air, clinched Henshaw's win in a "dramatic" final, Newport said.
Henshaw's score narrowly edged runner-up Brown, of the United States, a winter X-Games gold medallist, who returned to Wanaka this winter after he claimed titles at the Freeski Open and New Zealand Winter Games last year.
New Zealand hopes in the competition faded, when Wanaka freeskier Byron Wells failed to make it past the semifinals.
Top New Zealand 1 qualifier Taylor King, of Auckland, progressed to the finals to finish in 14th place overall.
Third place went to US freeskier Gus Kenworthy.
Canadian Kim Lamarre, put several earlier crashes behind her to successfully complete her final run of the day, which proved high-scoring enough to claim the women's title.
Lamarre pulled out a difficult trick in her last run to separate herself from the rest of the field, Newport said.
Australian skier Anna Segal came second, as Canadian Megan Gunning finished in third place.
The top New Zealand women were Mikey Austin, of Wanaka, who finished fifth and Kate Hartley, of Whakatane, who was sixth.
The NZ Freeski Open halfpipe competition is scheduled to start at 9.30am at Cardrona today with the men's qualifiers the first away.
