"They've got a strong side batting and bowling, Kane Williamson is their linchpin in the middle there and they've got bowlers who swing the ball", he said.
Finch won the toss and chose to bat first in seemingly ideal, sunny conditions at the "home of cricket".
Boult, however, made the breakthrough in the fifth over when Finch was plumb lbw to a ball that nipped back.
The express pace of Ferguson also contributed to Smith's downfall, the former captain falling for just five when he miscued a hook shot and Guptill, now at short fine leg, held a sensational diving catch as he atoned for his earlier misses in style.More news: Government Removes Migrant Children From Detention Facility After Reports of Dire Conditions
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Australia (Playing XI): Aaron Finch (C), David Warner, Steven Smith, Usman Khawaja, Glenn Maxwell, Marcus Stoinis, Alex Carey (WK), Pat Cummins, Mitchell Starc, Adam Zampa and Jason Behrendorff. Glenn Maxwell (1) also departed soon after, leaving Australia looking down the barrell at 92/5.
Smith looked stunned to be out by player standing where Guptill was and only Ben Stokes' remarkable catch for England against South Africa in the opening match of the World Cup would rival it.
New Zealand, third in the 10-team table with one match to go, have still not secured their place in the knockout phase. Ross Taylor (30) then skied a delivery that was caught by the keeper as the Kiwis lost way.
Gamechanger: The 107-run partnership between Alex Carey and Usman Khawaja stabilized the Australian innings at a time when it looked like they would struggle to reach even 200.
Boult's hat-trick was his second in ODI cricket. Carey joined Khawaja with the score at 92/5 and the side in deep crisis. Steve Waugh had recently called him a "hybrid between Michael Bevan and Michael Hussey".