''We were chasing a total that was certainly gettable if we were to play well - and we were far from playing well."
That said, Williamson, whose wicket at 74 for one last night started the rot, in which New Zealand lost nine wickets for 73 in 22.2 overs, admired Australia's cricket, the No 1 ranked team dealing to the No 3 pretenders emphatically.
''Australia were outstanding. They played three pretty complete performances.
''I guess in the first game and this one (last night) we were able to take wickets but there was one constant of a guy going on to get a hundred.
''Their bowling throughout the series was very good.
''From our perspective in any chase you want to provide more resistance in order to take the game deeper. We certainly didn't have that."
Williamson defended his players on the score of determination.
''It's certainly not through lack of trying," he said.
''When you're playing a very good team like Australia, who are playing some of the best one-day cricket going around, particularly in this series, that is a challenge.
''We'll be on a flight (this) morning and a lot of guys will be thinking about this series and there's a lot of opportunities to become better for it.
''They were very clinical in everything they did throughout this series. It's important we take bits of the way they played their cricket; their accuracy in how they skinned it."
Australian skipper Steve Smith, along with opener Warner, the batting kingpins of a side New Zealand's bowlers were unable to corner, was chuffed with the quality of their performances.
''The guys in the top four, we've had three games where guys have scored hundreds and the bowlers have executed their plans beautifully.
"I'm just proud of the way our guys played after a tough tour to South Africa where we lost 5-0. It was nice to turn things around and win every game in this series."
New Zealand will get a chance to regain the trophy when Australia return for another three ODIs in early February. But if they don't pick their game up significantly they run the risk of more disappointment.
The final defeat was perhaps the most dispiriting.
In game one, they were chasing 325 and had a chance of catching it; in Canberra, they let Australia run up 378 from which there was no comeback.
But last night, the bowlers and fielders stepped up after two ordinary efforts, only for the batsmen to trip up, against tough bowling from Mitchell Starc and some gentle spin from Travis Bird - yin and yang proving too much last night.
New Zealand now head home to face Bangladesh from Boxing Day. The challenge will be far less intense and it represents a chance to get back to winning ways. But the scars of this trip may last a while yet.
