Williamson has batted till the end and helped New Zealand to win a thrilling game by the narrowest of margins of one wicket against Australia at Eden Park.
The world cup, which has been seen tons of runs has presented a nail-biter which had only about 150 per innings.
New Zealand reached 152 off 23 overs losing nine wickets in the after Williamson slammed a six straight down the ground to traverse the Australian score of 151.
Starc took the wicket of Southee for duck moments after Cummins dismissed Vettori for duck.
Starc's wicket deserving delivery sent Ronchi back to the pavilion at 6 moments after Maxwell took the wicket of Anderson at 26.
Australian paceman Starc removed Elliott right after break while skipper Brendon McCulam was caught at mid-off in the bowling of another paceman Pat Cummins after a swashbuckling 50 off just 24 balls in order to chase the 152 runs total.
Ross Taylor followed his captain as he was bowled by Starc at the first ball of 9th over for just one run.
Earlier, Starc sent opener Guptill back to the pavilion at 11 in one of the most anticipated group stages matches of the world cup between the two co-hosts.
The Aussies could only manage to score 151 in 32 overs after losing all the wickets in the World Cup match against New Zealand at Eden Park.
The eagerly anticipated trans-tasmanian derby has gained more heat as according to the pre-tournament speculations this fixture could be replicated in the final.
New Zealand have been showing inch perfect show till now in this tournament due to some outsanding performances of their players.
One of them, fast bowler Trent Boult terrorised through the Austrailan batting and picked up a five-for. The southpaw had a fascinating figure of 27-5 from his ten overs.
The opening bowler returned for his second burst and just ran through the famed Australian batting line-up. The left-arm pacer sent back Maxwell and Marsh in one over.
Clarke was battling it out, but he too succumbed to the attacking fields set by B-Mac. Boult, then registered his maiden ODI 5-wicket haul by ripping through Johnson and Starc.
Haddin then hit a few meaty blows to give some respectability to the score. Nonetheless, it is still Australia's lowest score in World Cups batting first.
Southee sent Finch and Warner back to the pavilion. Vettori took the wickets of Watson and Smith, compeling Australia into a tight spot in the heavyweight battle of the hosts at World Cup 2015. Anderson dismissed Haddin at 43 in the one-sided affair.
Earlier in the day, Australia won the toss and opted to bat first.
The setting for this hugely anticipated contest between the co-hosts of the World Cup was perfect.
Auckland's weather was sunny and Eden Park was steadily filling up to an expected full house as Australia's returning captain Michael Clarke chose to bat.
Brendon McCullum said he would have bowled.
Both teams had named their XIs on the eve of the game. Clarke took George Bailey's spot in Australia's side, and they picked the extra pace of Pat Cummins over the control Josh Hazlewood offers. New Zealand were unchanged for their fourth consecutive game.
A New Zealand victory will cement their place in the Wellington quarter-final, and make them favourites to top Group A.
Australia were playing their first match in two weeks, having beaten England on the opening day of the World Cup before enduring a washout against Bangladesh in Brisbane the following Saturday.
The World Cup is yet to have a competitive match between two full members and it is hoped that the form of these two sides - Australia and New Zealand have won their last five completed games - will end that disappointing run.
New Zealand: 1 Martin Guptill, 2 Brendon McCullum (capt), 3 Kane Williamson, 4 Ross Taylor, 5 Grant Elliott, 6 Corey Anderson, 7 Luke Ronchi (wk), 8 Daniel Vettori, 9 Adam Milne, 10 Tim Southee, 11 Trent Boult
Australia: 1 David Warner, 2 Aaron Finch, 3 Shane Watson, 4 Michael Clarke (capt), 5 Steven Smith, 6 Glenn Maxwell, 7 Mitchell Marsh, 8 Brad Haddin (wk), 9 Mitchell Johnson, 10 Mitchell Starc, 11 Pat Cummins
