Mitchell Santner heaped praise on Jacob Duffy, who took three wickets as New Zealand posted an eight-run win against Sri Lanka in the first T20I on Saturday.

In a crucial 14th over, Duffy dismissed Kusal Mendis (46), Kusal Perera (0) and Kamindu Mendis (0) to spark Sri Lanka's collapse after the visitors had reached 121 without loss.

Despite Pathum Nissanka's 60-ball 90, Sri Lanka only managed 164-8 in 20 overs to concede the opening match.

Batting first, half-centuries from Daryl Mitchell (62) and Michael Bracewell (59) had helped New Zealand recover from 65-5 after nine overs to a competitive total of 172-8.

Sri Lanka then looked to be cruising to a victory in the first of three T20Is in Mount Maunganui before Duffy's decisive over turned the tide in the game.

"It was a game of two halves. When you lose wickets in clumps, it is hard to get starts. But it was a massive partnership [between Mitchell and Bracewell] for us," said New Zealand captain Santner after the game.

"They soaked up the pressure and then put it back on to put up a pretty good score. Then it was about whether we can try to take wickets."

"The run rate was around eight, but we did some aggressive bowling with aggressive fields, and mid-wicket up. Duffy changed the game for us," Santner said.

Duffy finished the game with figures of 3-21 while Matt Henry (2-28) and Zakary Foulkes (2-41) also stemmed the flow of runs with wickets.

Meanwhile, Sri Lanka skipper Charith Asalanka expressed his disappointment following the defeat.

"I am very disappointed because we should have done better. Pathum and Kusal batted well but the rest, including me, should take responsibility for this loss," Asalanka said.

"We hope to come back really well. I thought we could have done better in bowling and fielding, but it was a decent pitch and when the openers were batting, it looked easy."

The two teams will meet again at the same venue on Monday for the second T20I.