21 year old Munn, from the Manawatu Golf Club in Palmerston North, completed his most significant amateur victory although he is a previous winner of two 72 hole Charles Tour professional events in New Zealand.
"I was so much in the zone I didn't feel the rain," said the New Zealand rep, who finished runner up at the Argentine Amateur late in 2012.
"This is easily my most important win."
Cameron Smith finished alone in 4th position one shot behind Kimsey and Drewitt with Brady Watt 5th.
Most of the players involved this week will now head south to play the NSW Amateur Championship to be staged over three courses, the Coast Golf Club, the Bonnie Doon Golf Club and the Royal Sydney Golf Club.