Having been sent in, New Zealand piled on 331 for six before dismissing Sri Lanka for 234.
The batting effort was impressive, with an opening stand of 111 between captain Brendon McCullum and Martin Guptill, who made 65 and 49 respectively.
Kane Williamson, although scratchy early on, capitalised on being dropped twice to make 57, his 13th time past 50 in his last 17 ODI innings.
Grant Elliott and Corey Anderson picked the tempo up after Williamson and Ross Taylor were out in consecutive balls. Anderson and Luke Ronchi were then largely responsible for 102 runs being flayed off the last 10 overs.
Anderso flogged 75 off 46 balls, being out off the last ball of the innings; Ronchi was left on 29 off 19 balls.
The threat expected from seamer Lasith Malinga never materialized as he was hit for 84 in his 10 overs while Nuwan Kulasekara's eight overs cost 78.
Sri Lanka made an encouraging start, with Lahiru Thirimanne stroking a fine 65.
However the loss of three wickets for five in 12 balls - including the crucial one of Mahela Jayawardene for a duck - undermined the Sri Lankans.
Kumar Sangakkara looked likely in getting to 39 in 37 balls, before missing a Trent Boult full toss to be lbw.
From there the task was beyond captain Angelo Mathews, who made 46, but with little support.
Boult, Dan Vettori, with an impressive two for 34 off 10 overs, Adam Milne, Tim Southee and Corey Anderson all took two wickets as New Zealand kicked off their campaign in style.
They next meet Scotland in Dunedin on Tuesday while the Sri Lankans play Afghanistan, also in Dunedin, on February 22.
- by David Leggat of the New Zealand Herald
New Zealand innings highlights
1st over: New Zealand captain Brendon McCullum strikes the first ball he receives in the tournament for four over extra cover off Nuwan Kulasekera. NZ: 0-6
2nd over: McCullum takes another boundary through the covers, this time off the back foot, in Lasith Malinga's first over after a lengthy injury layoff. NZ: 0-15
5th over. Martin Guptill strikes consecutive boundaries, glancing Kulasekera to fine leg then clipping a short delivery through cover point. NZ: 0-38
8th over. McCullum crashes successive fours through the leg side as Malinga strays in length then hits a no ball straight back over the bowler's head for six. Another four follows with a slice to third man followed by a controlled push through mid-wicket for a further boundary. NZ: 0-68
10th over. Left-arm spinner Rangana Herath takes over from Malinga and strikes a good length immediately, conceding only four runs, all singles. NZ: 0-77
12th over. Herath twice appeals unsuccessfully for lbw against McCullum pushing forward. The batsman responds with his eighth four to bring up his half-century from 35 deliveries. NZ: 0-87
14th over. McCullum strikes another four off Herath to take New Zealand to 100 from 82 balls. NZ: 0-103
16th over. McCullum attempts to loft Herath for six but Jeevan Mendis holds a good catch leaping high just inside the long-off boundary to dismiss the New Zealand skipper for 65 off 49 deliveries with 10 boundaries and a six. NZ: 1-111.
17th over. Kane Williamson on nought is dropped by wicketkeeper Kumar Sangakkara diving to his right off the first ball of paceman Suranga Lakmal's first over. NZ: 1-112
19th over. Williamson collects a streaky four off Lakmal when an inside edge from an attempted cut flies past Sangakkara. NZ: 1-122
20th over. Herath continues to vary his flight and pace skilfully, beating Guptill with a delivery which hit the batsman's pads but was going too high to hit the stumps. NZ: 1-127
23rd over. Guptill unleashes an imperious hook off Lakmal which flies to the boundary but is then dismissed one short of his half-century when he edges a delivery to Sangakkara who takes the ball in both hands diving to his right. NZ: 2-126
27th over. Williamson and the new batsman Ross Taylor consolidate against some accurate bowling from Herath and Lakmal, bringing up the 150 from 161 deliveries. NZ: 2-151
30th over. Kulasekera returns to the attack and Williamson survives a second chance when Mathews fails to hold on to a fierce drive at short extra-cover. Williamson celebrates with an elegant pull shot to the boundary in the next over from the Sri Lanka captain. NZ: 2/166
32nd over. Williamson hoists Kulasekara to leg for four then plays a splendid off-drive for six which a jubilant spectator catches with his right hand. He brings up his 13th half-century in his last 17 one-day internationals from 59 balls with a push for two. NZ: 2-183
34th over. Williamson is finally dismissed for 57 when Dimuth Karunarathne takes a spectacular diving catch at wide long-on off Mendis. Ross Taylor is then stumped by Sangakkara off the next delivery from the leg-spinner for 14. NZ: 4-193
37th over. New Zealand take the batting powerplay and Grant Elliott sweeps Dilshan fine for four to bring up the 200. Corey Anderson slams a six over the bowler's head as the home side seek to accelerate. NZ: 4-210
40th over. Malinga returns with improved accuracy and length and the batsmen are restricted to singles. NZ: 4-229
44th over. Elliott falls for 29, caught at mid-wicket by Lahiru Thirimanne off a full toss from Lakmal. NZ: 5-259
46th over. Luke Ronchi glides Malinga off his hips for four to fine-leg and steers a delivery square on the off for another boundary. Anderson crashes two brutal fours off Lakmal and is then dropped in the covers by Mendis when the ball goes straight through the fielder's hands. NZ: 5-287
47th over. Malinga knocks Ronchi's off stump out of the ground but television replays shows the delivery was a no ball and the batsman, who was halfway back to the pavilion, is recalled. NZ: 5-294
48th over. Anderson reaches his half-century from 36 deliveries with a powerful off-drive to the boundary off Kulasekera. He celebrates with six over the bowler's head which brings up the New Zealand 300. NZ: 5-308
50th over. Anderson is caught off the last ball of the innings for 75 by Lakmal in the covers after the fielder juggles the ball. Ronchi finishes on 29 not out after a sixth-wicket partnership of 73 from 38 balls. NZ: 6-331
Sri Lanka innings highlights
2nd over: Tillakaratne Dilshan and Lahiru Thirimanne get the Sri Lanka innings underway with boundaries off Trent Bolt's opening over. Dilshan, though, is lucky to get away with a inside edge which evades the stumps. SL: 0-13
8th over: Bolt takes further punishment from left-hander Thirimanne who takes boundaries from successive balls both sides of the pitch. SL: 0-37
10th over: Adam Milne takes over from Bolt and the fast bowler's first delivery catches the edge of Dilshan's bat and flies to third man for a single. SL: 0-46
13th over: Veteran left-arm spinner Daniel Vettori makes the breakthrough in his second over after replacing Tim Southee when Dilshan pushes a full-length delivery tamely back to the bowler after scoring 24 from 41 balls. SL: 1-67
17th over: Kumar Sangakkara plays a sumptuous cover-drive to the boundary off Milne and leg-glances the next delivery for four. Grant Elliott replaces Vettori and Thirimanne lobs the ball just over the leaping Brendon McCullum at silly mid-on. Thirimanne reaches his fifty in the same over from 45 deliveries with seven fours. SL: 1/91
20th over: Boult returns and Sangakkara moves smoothly down the pitch to hit the left-arm paceman over mid-off for four. SL: 1-112
22nd over: Boult returns to give New Zealand an important wicket when a late outswinging yorker knocks Thirimanne's off stump out of the ground. Thiramanne had made 65 from 60 balls with eight fours and his partnership with Sangakkara had put Sri Lanka firmly in contention. SL: 2-124
23rd over. McCullum brings Vettori back into the attack and Mahela Jayawardene edges a simple catch off the final ball to wicketkeeper Luke Ronchi and is out without scoring. SL: 3-125
24th over. Boult strikes again, dismissing Sangakkara lbw for 39 with a full inswinger which the batsman missed completely. Sangakkara asks for a review but the replay shows the ball would have hit near the bottom of the middle stump. Three wickets have fallen in as many overs. 4-133
30th over. Vettori's guile and Boult's late movement continue to restrict Sri Lanka and, although captain Angelo Mathews and Dimuth Karunaratne take the total past 150, the required run rate climbs to more than eight an over. 4-155
32nd over. Milne clean bowls Karunaratne for 14. Jeevan Mendis (4) can make little of the New Zealander's pace and hostility and edges the final ball of the over to Ronchi. SL: 6-168
35th over. Vettori delivers another immaculate over to finish with two for 34 from his 10 overs. SL: 6/179
39th over. Corey Anderson bowls his first over of the tournament and is denied a wicket from his fourth ball when Ross Taylor spills a simple chance at slip off Nuwan Kulasekera. In his next over the burly left-arm paceman is rewarded when Kulasekera (10) slices an easy catch to Elliott at deep cover. SL: 7/201
40th over. Mathews, Sri Lanka's last recognised batsman, takes his total to 45 but he is unable to strike the boundaries necessary to give his team a decent chance of recording a sixth successive World Cup win over the New Zealanders. SL: 7-209
42nd over. Mathews, Sri Lanka's last recognised batsman, is well caught by Vettori running in at mid-on for 46 after lofting an attempted hook off Southee. Southee follows up by dismissing Lasith Malinga, caught behind by Ronchi, for a duck in the same over. SL: 9-218
46.1 overs. New Zealand complete a 98-run victory by dismissing Sri Lanka for 233. Rangana Herath is the last batsman to go, caught at cover by Adam Milne off Anderson for 13. SL 233 all out.
- NZ Herald/Reuters
New Zealand: Brendon McCullum (c), Martin Guptill, Kane Williamson, Ross Taylor, Grant Elliott, Corey Anderson, Luke Ronchi, Dan Vettori, Adam Milne, Tim Southee, Trent Boult.
Sri Lanka: Angelo Mathews (c), Tillekaratne Dilshan, Dimuth Karunaratne, Kumar Sangakkara, Mahela Jayawardene, Lahiru Thirmanne, Jeevan Mendis, Nuwan Kulasekara, Rangana Herath, Lasith Malinga, Suranga Lakmal.
