Although Sri Lanka's senior player Mahela Jayawardena scored a century, the Kiwis ripped through the lions' batting line, limiting their score to 218.
The home team reached the target in the 43rd over with 3 wickets to spare.
Scores
Sri Lanka (50 overs) 218/9
Mahela Jayawardena 104, Lahiru Thirimanna 23, Ajantha Mendis 23
Mitchell McClenaghan 4-36
New Zealand (43 overs) 219/7
Brendan McCullum 51, Corey Anderson 81
Nuwan Kulasekara 2/43, Sachithra Senananayake 2/43