A six-wicket haul for Trent Boult and a Ross Taylor century brought New Zealand a 24-run victory over Australia in the third one-day international Sunday to win the series 2-0.
Their masterclass saw New Zealand reclaim the Chappell-Hadlee Trophy while Australia lost their outright hold on the world number one ODI ranking.
They slipped to 118 points, equal with South Africa, who beat Sri Lanka in Johannesburg on Saturday to go 3-0 up.
South Africa will overtake Australia if they win the remaining two matches in that series.
New Zealand made 281 for nine, and although Australian captain Aaron Finch felt the target was gettable they were bundled out for 257 with three overs remaining.
Williamson won the toss and had no hesitation in batting first on the Hamilton wicket, correctly forecasting it would slow up as the day wore on and Boult would come into his own.
But given the prime early batting conditions, New Zealand appeared to have under-performed despite Taylor's 107 off 101 balls and his century partnership with Dean Brownlie, who made 63.
With rankings and the series at stake after New Zealand won the first ODI by six wickets and the second was washed out, Finch and Shaun Marsh made a flying start to Australia's reply, averaging more than six an over.
They were particularly harsh on Tim Southee, whose opening four-over spell cost 30 runs, while new ball partner and man-of-the-match Boult had one for 10 at the time.
Marsh was first to fall, run out for 22, and Peter Handscomb was bowled first ball by Boult.
[caption id="attachment_44715" align="aligncenter" width="512"]
Australian Glenn Maxwell (C) is dismissed as New Zealand celebrate during the one-day international cricket match between New Zealand and Australia at Seddon Park in Hamilton AFP
Finch and Travis Head continued the charge with a 75-run stand for the third wicket before New Zealand broke through with their second two-wicket burst.
Williamson had Finch caught by Boult at deep midwicket for 56 and Glenn Maxwell was caught behind off Mitchell Santner without getting on the board, leaving Australia 120 for four.
Head and Marcus Stoinis looked to have the run chase under control in a 53-run partnership, until Boult came back for his second spell and claimed Head for 53 and James Faulkner for nought in the space of four balls.
Stoinis pressed on to 42 before Santner claimed his wicket, while Mitchell Starc, who scored 29 not out, and Pat Cummins' 27 took Australia to within 32 runs of their target at 249 for seven.
But Boult broke through again to claim the last three wickets in his final two overs and finish with six for 33.
Taylor was key to the New Zealand innings as he equalled Nathan Astle's New Zealand record of 16 ODI centuries.
New Zealand 281 for 9
(Taylor 107, Brownlie 63, Faulkner 3-59, Starc 3-63) beat Australia 257
(Finch 56, Head 53, Boult 6-33) by 24 runs