Poor Sri Lanka collapse to 8-4 early before being bowled out for 102
Brilliant Boult takes 4-13
Phillips, dropped on 12 and 45, brings up stunning century off 61 balls before falling for 104
NZ recover from 15-3 to post 167-7
Group 1 leaders NZ now on five points, two clear of England, Ireland and Australia
A glorious shot from Glenn Phillips to get himself off the mark, driving fluently through the covers for New Zealand's first boundary.
They still have plenty of batting so won't be panicking yet, but it's certainly made things interesting.
Henry Moeran
BBC Test Match Special commentator
To have taken the big wickets of Allen and Conway creates a bit of stress and nervousness for New Zealand.
Alex Hartley
Former England bowler on BBC Test Match Special
The dangerous opening batters are out. Sri Lanka have opened this game right up.
Conway b Dhananjaya 1 (NZ 7-2)
Well! This is unexpected!
New Zealand's Mr Consistent, who made 92 from 58 balls in their thrashing of Australia, has gone for just a single.
Conway is bowled trying to give himself some room and hit the spinner through the off side, and Sri Lanka's joy continues.
Another very good over for Sri Lanka, just three singles from it.
They'll be delighted with this start. Can they maintain it for the rest of the powerplay?
Henry Moeran
BBC Test Match Special commentator
This will give real belief to Sri Lanka because they knew they had to break that partnership.
Alex Hartley
Former England bowler on BBC Test Match Special
Brilliant over from Sri Lanka. To get the wicket of Finn Allen is a huge wicket. He just misread that seam up delivery.
Kane Williamson is in early, and takes a single from his first ball to calmly get off the mark.
The perfect start for Sri Lanka.
Alex Hartley
Former England bowler on BBC Test Match Special
Finn Allen has gone back to a delivery that he should have been forward to. He played so well against Australia and blew the competition wide open but he has to go early.
That 200 you saw New Zealand get against Australia, you almost think it has gone already.
Henry Moeran
BBC Test Match Special commentator
A big wicket early in the game, we're not going to see that rocket-powered start from New Zealand today. Finn Allen just didn't pick it.
Allen b Theekshana 1 (NZ 2-1)
The spin does the trick! A big early breakthrough for Sri Lanka!
It's almost like an inswinger from Theekshana, nipping between Finn Allen's defences as he goes to play off the back foot.
No Finn Allen fireworks tonight. Sri Lanka are, quite rightly, buzzing with that one.
Stuart Clark
Former Australia fast bowler on Test Match Special
The biggest trick for New Zealand is to start again, don't go out thinking you're already 200-3 as they got against Australia. If things don't quite their way to start with, don't panic, take a moment to reassess.
Sri Lanka on the other hand will be after a couple of early wickets. But I sense that New Zealand are primed for this.
Will be interesting to see how Finn Allen plays the spin having blasted Australia's seamers around the park the other night.
He starts cautiously though, solid in defence from the first ball.
It's time for my obligatory mention of how much I love New Zealand's kit, and also to note that Sri Lanka's national anthem has got to be up there with the best (after Wales, obviously).
Anyway, let's get going with the actual cricket. Finn Allen and Devon Conway are opening up for New Zealand, and Sri Lanka are opening with spin in the form of Maheesh Theekshana.
A complicated question, to be honest.
New Zealand are top with a brilliant run-rate, and England are second but they still need to win their remaining games to qualify. Australia need to win big, and hope England slip up.
Alex Hartley
Former England bowler on BBC Test Match Special
Sri Lanka's loss to Namibia set the tone for this tournament. Anything can happen, it's been brilliant. Everyone has been beating everybody. Who would have thought Zimbabwe would beat Pakistan? This tournament keeps providing.
New Zealand: Devon Conway (wk), Finn Allen, Kane Williamson (capt), Glenn Phillips, Daryl Mitchell, Jimmy Neesham, Mitchell Santner, Ish Sodhi, Tim Southee, Lockie Ferguson, Trent Boult.
Sri Lanka: Pathum Nissanka, Kusal Mendis (wk), Dhananjaya de Silva, Charith Asalanka, Banuka Rajapaksa, Dasun Shanaka (capt), Wanindu Hasaranga, Chamika Karunaratne, Maheesh Theekshana, Lahiru Kumara, Kasun Rajitha.
Sri Lanka captain Dasun Shanaka: "We would have had a bat first as well.
"[The Australia defeat] It was just one game. Our spinners are key for us, but for the team it was a bad day.
"We will do what we have to do today to win."
New Zealand captain Kane Williamson: "It looks like a good surface. We've played here once before and want runs on the board.
"It feels like we haven't played for a while so it's nice to get back out here and it's important for us to just focus on our plans.
"The thing is with these tournaments, it's different opposition on different days and different grounds so we just make those assessments again and as a batting unit and a bowling unit, just apply ourselves."
Image source, Getty ImagesKane Williamson wins the toss and opts to have a bat first on what he says looks like a very good pitch in Sydney.
They racked up 200 against Australia here in their first game, so no surprises to see confidence in their batting line-up.