"We went in with plenty of confidence and good wins under our belt, but we knew it all meant nothing come today," allrounder Corey Anderson said. "We know it's early stages, and there's a long road to go. We'll take everything in our stride, and push on to Scotland [in Dunedin on Tuesday]."
Openers Brendon McCullum and Martin Guptill got the innings off with plenty of zing, putting on 111 in 15.5 overs.
McCullum really is remarkable, unlike any other batsman in the game. He uses the crease simply as a reference point, then his dancing feet take him to places other batsmen only dream of and certainly don't act on.
His 65 in 49 balls set the tempo. Guptill's 49 impressed, too, with several handsome, authoritative strokes in his 100th ODI appearance.
There was a stutter mid-innings but the way it was put back on track gave the impression of a team well in control of their strategies and high on self-assurance.
Kane Williamson was scratchy early. He was dropped on 0 - a hard, low chance to wicketkeeper Kumar Sangakkara - and then dropped on 28 by Angelo Mathews.
But he eventually got going before falling to a spectacular diving catch by Dimuth Karunaratne at wide long on, having achieved a 13th score past 50 in his last 17 innings.
A ball later, Ross Taylor overbalanced and was stumped.
Now came the important period. There have been many times when the good work would have been wasted. Not now. Grant Elliott and Anderson ticked along at a run-a-ball, before the last 10 overs and a barrage of runs.
Anderson hit with tremendous power, hurtling to 75 off 46 balls. Luke Ronchi provided just the right pep from the other end, but you had to wonder at some of captain Mathews' bowling choices.
Lasith Malinga, well underdone but essential at the World Cup when fit, went for 84 " feeling McCullum's heat early. Nuwan Kulasekara conceded 78 off eight.
Yet Mathews ignored Jeevan Mendis' leg spin after he took two wickets in his second over, the tidy Rangana Herath didn't bowl his overs out and Mathews himself rolled his arm for just six.
Lahiru Thirimanne batted beautifully for 65 and Sangakkara was sailing along when he got in a tangle to a Boult full toss.
Three wickets fell in 12 balls " the key veteran Mahela Jayawardene for a duck " and Mathews could not do the job on his own.
Scoreboard
Scoreboard from the opening World Cup one-day game between New Zealand and Sri Lanka at Hagley Park in Christchurch.
New Zealand
Guptill c Sangakkara b Lakmal 49
McCullum c Mendis b Herath 65
Williamson c Karunaratne b Mendis 57
Taylor st Sangakkara b Mendis 14
Elliott c Thirimanne b Lakmal 29
Anderson c Lakmal b Kulasekara 75
Ronchi not out 29
Extras (2lb, 8w, 3nb) 13
TOTAL (for 6 wickets) 331
FOWs: 1-111, 2-136, 3-193, 4-193, 5-258, 6-331.
Bowling: Kulasekara 8-0-78-1 (3w), Malinga 10-0-84-0 (3w, 3nb), Mathews 6-0-28-0, Herath 9-0-37-1 (1w), Dilshan 5-0-35-0 (1w), Lakmal 10-0-62-2, Mendis 2-0-5-2.
Sri Lanka
Thirimanne b Boult 65
Dilshan c and b Vettori 24
Sangakkara lbw b Boult 39
Jayawardene c Ronchi b Vettori 0
Karunaratne b Milne 14
Mathews c Vettori b Southee 46
Mendis c Ronchi b Milne 4
Kulasekara c Elliott b Anderson 10
Herath c Milne b Anderson 13
Malinga c Ronchi b Southee 0
Lakmal not out 7
Extras (10w, 1nb) 11
TOTAL (all out, 46.1 overs) 233
FOWs: 1-67, 2-124, 3-125, 4-129, 5-163, 6-168, 7-196, 8-216, 9-217, 10-233.
Bowling: Southee 10-1-43-2 (2w), Boult 10-0-64-2, Milne 10-0-56-2 (3w, 1nb), Vettori 10-0-34-2 (2w), Elliott 2-0-11-0, Williamson 1-0-7-0, Anderson 3.1-0-18-2 (3w).
Result: New Zealand won by 98 runs.
Umpires: Marais Erasmus (South Africa) and Nigel Llong (England).
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