New Zealand captain Stephen Fleming said the collapse in Australia's one-day form meant the World Cup starting next month is wide open.

The five-wicket defeat of the world champions in Auckland on Sunday was the first time in ten years that Australia had lost four one-day matches in a row, and meant they relinquished the top spot in the rankings, to South Africa, for the first time.

New Zealand reached 337 for four to achieve the second highest run chase in history with eight balls to spare to secure the Chappell-Hadlee Trophy.

The Kiwis won the first match of the series in Wellington on Friday by ten wickets, the first time Australia had ever lost by such a margin.

"I think that's just where international cricket is at the moment, we're going to a World Cup with teams beating each other," Fleming told reporters after the epic win.

"I guess that's the exciting thought, and the scary thought, that on any given day one of eight teams could win this World Cup."

Having looked dominant in the group stages of the tri-series against England and New Zealand, the Australians have suffered injuries and a collapse in form.

They lost the finals 2-0 to England and have lost Brett Lee and Andrew Symonds to injuries that could rule them out of the Mar 14-Apr 28 World Cup in the Caribbean.

Skipper Ricky Ponting and Adam Gilchrist were rested for the short New Zealand trip, and the Australians have struggled under stand-in skipper Mike Hussey despite fielding a strong bowling line-up.

"I don't think the world is focussing on Australia. I think there are other teams in West Indies conditions that will be just as dangerous," Fleming added.

"The South Africans are playing well, we've watched a bit of it through Australia and they've certainly got the wood on Pakistan.

"They're one of a number of teams that can win this World Cup. I have no doubt that they'll be there or thereabouts."

The final match of the Chappell-Hadlee Trophy series is at Hamilton's Seddon Park on Tuesday.