Martin Guptill believes New Zealand are capable of building the momentum that can turn them into genuine World Cup contenders.

New Zealand, runners-up four years ago, started their 2019 campaign with a crushing 10-wicket win over Sri Lanka in Cardiff.

Sri Lanka were bundled out for just 136 on a green-tinged surface as Matt Henry's seam movement and Lockie Ferguson's raw pace proved too much for them.

Both New Zealand bowlers took three wickets apiece before Guptill (73 not out) and fellow opener Colin Munro (58 not out) raced to the victory target in just 16.1 overs.

"You want to build that momentum early," said Guptill, who admitted that it was an important toss to win with early overhead conditions also assisting the bowlers.

"Our bowlers did that from the front and made it difficult for Sri Lanka.

"If we bowl first in the next few games then hopefully we can continue to do that.

"And if we come out with a bit of freedom with the bat like we did, I think we can have a successful tournament."

New Zealand are keen to make a fast start to the tournament given the make up of their fixture list.

The Black Caps' next two games are against Bangladesh and Afghanistan, with arguably their toughest games at the back end of the round-robin format.

New Zealand's final two group games are against great rivals Australia and competition favourites England.

"The beauty of our guys is that they can exploit those conditions quite regularly," Guptill said.

"They bowled in the right areas right away to get the rewards up front.

"It's always nice to have a healthy run rate at the start of the tournament.

"We had them seven or eight down and wanted to knock them over as quick as possible, and then get the runs quickly as well.

"We've got a healthy run rate at the moment and hopefully we can take that through the rest of the tournament."

Sri Lanka came into the World Cup with internal divisions in the camp and having lost nine of their last 10 one-day international series.

Dimuth Karunaratne took over the captaincy from Angelo Mathews after a four-year ODI exile, but little is expected of the 1996 champions.

Sri Lanka partially recovered from 60 for six, but they were dismissed in 29.2 overs as Karunaratne became only the second batsman in World Cup history to carry his bat through a completed innings.

"The toss was a crucial part, but you have to give New Zealand credit for the way they bowled," said Karunaratne, who made an unbeaten 52.

"We could not build partnerships and we kept losing wickets.

"I think 240-250 would have been a good score in those conditions, it wasn't a 300 wicket.

"We have to keep our chin up now and I'm sure that if we can build some good partnerships we can do well."

Sri Lanka's large contingent of fans were clearly disappointed with their team's performance and made their feelings known at the end of the game.

Boos were directed towards the Sri Lanka players and Karunaratne said: "They have come far and spent their money and come here to see a good match.

"They will want to win with us. Losing doesn't matter but we need to give a good fight. That's the main thing.

"One hundred and thirty runs is no match. It's not a game. So we need to give a good show."