Boult later returned to end a promising fourth-wicket partnership between de Kock and Heinrich Klaasen, who was caught behind for 39.
South Africa were in a strong position as the rain set in - de Kock was not out on 84 and looking to launch the South African innings but the rain would not subside and play was abandoned.
Trent Boult was the pick of the New Zealand bowlers before play was stopped, taking two wickets for 20 off five overs.
The Black Caps were declared victors following the Duckworth Lewis calculations.
Both sides will next be in action when the competition is underway. New Zealand entertain England in the opener on Thursday while South Africa begin their campaign against Sri Lanka on Saturday.