"It was an excellent effort from our guys to be able to manufacture a win from nowhere really," captain Brendon McCullum said last night.
Among the planks in New Zealand's strong surge up the ladder is their fielding, which again was exemplary.
By contrast Sri Lanka were dreadful, spilling four catches from Williamson on his way to a career-high 242 not out.
"We took our chances brilliantly," McCullum said.
"We've got a very good fielding group and we work very hard on our fielding ... That's an area we can steal a march on opposition teams."
New Zealand now go into World Cup preparation mode, starting with a seven-game ODI series against the Sri Lankans that begins in Christchurch on Sunday. The squad of 15 will be named today.
"This is going to be a huge period in their lives for the players named," McCullum said.
New Zealand will play test series in England and Australia in the second half of this year.
"They will be tough tours but certainly something that the guys will be looking forward to," McCullum said. "We should head over there with some confidence."