Kane Williamson's half-century and a spin bowling assault fired New Zealand to a 35-run win over Ireland at the Adelaide Oval on Friday.
New Zealand's batsmen posted an imposing 185 for six after Ireland elected to field before the Black Caps' bowlers restricted the Irish to 150 for nine.
The win saw Williamson's team cement the top spot in Group 1 with seven points and a huge run-rate advantage over second-placed England and third-placed Australia.
Ireland bowed out of the World Cup but head home with pride after a solid tournament capped by a sparkling hat trick to paceman Josh Little.
Left-arm fast bowler Little had captain Williamson caught for 61, then trapped both James Neesham and Mitchell Santner lbw for no score in the 19th over to bring up Ireland's second hat-trick in T20 internationals.
However, the damage had already been done by Williamson and middle-order batsman Daryl Mitchell (31 not out).
Paul Stirling and Andy Balbirnie gave Ireland a fighting chance but left-arm spinner Santner broke the 68-run partnership when he had Balbirnie chopping onto his stumps.
Santner and legspinner Ish Sodhi then rattled through the top order, grabbing two wickets each to suck the life out of the Irish innings.
"We knew the spin would really come into the game and they bowled beautifully well," said Williamson.
"A good team effort, really."
Paceman Lockie Ferguson finished with an economical 3-22 after Ireland's chase unraveled.
Later in the day, New Zealand became the first team to book a semifinal berth in the T20 World Cup after Australia were restricted to 168-8 by Afghanistan in a crucial game.
After New Zealand beat Ireland by 35 runs in their final super 12 group, defending champions Australia needed to win against Afghanistan by an improbable 185 runs to overtake the net run rate of their Trans-Tasman rivals.
The hosts, however, scored 168 for 8 after being invited to bat by Afghanistan, paving the way for New Zealand to qualify for the knockout stage.
Australia now will need to limit Afghanistan to 106 or lower to stay alive in the semifinal race, which also involves England.
The win over Ireland saw New Zealand grab the top spot with seven points and a net run rate of +2.113. England (5 points), who will take on Sri Lanka in their final Super 12 game, are currently in the second spot with a run rate of +0.547.
Australia are placed third, also with five points, but with a run rate of -0.304. If they can restrict Afghanistan to 106 or lower, they can get past England's NRR.
New Zealand, led by Kane Williamson, began their campaign in the T20 showpiece with a dominating 89-run win over Australia, before thrashing Sri Lanka by 65 runs following a washout against Afghanistan.
Their only loss was against England by 20 runs at Gabba in Brisbane.
New Zealand had reached the final of the last edition, where they lost to Australia by eight wickets.
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