Colin Munro strikes another six during his record-breaking innings

When Martin Guptill walked from the Eden Park pitch having hit a New Zealand record for the fastest Twenty20 fifty, he could not have imagined that it would be bettered just 16 minutes later.

But that's what his replacement at the crease, Colin Munro, did - and he gave the Guptill record a wallloping.

While Guptill hit his 50 in 19 balls, Munro smacked his 50 in just 13 balls - polishing it off with a huge six to give the Black Caps an emphatic victory over hapless Sri Lanka in the second T20 international at Eden Park on Sunday.

Hannah Peters Colin Munro acknowledges the crowd after hitting a six for victory

Chasing 143 for victory, the Black Caps needed just 10 overs to reach their target and secure a 2-0 series triumph.

Munro, on trial for the No 3 spot in the New Zealand World T20 team, said it was nice to walk out with the freedom to express himself in the way he knows best.

"I was just absolute clear-minded, you're not actually thinking about, you're not trying to pre-meditate.

Hannah Peters Martin Guptill unleashes another huge six during his batting blitz.

"It was just waiting for the ball to be in my zone and watch the ball as hard as you can and swing hard."

"I've shown glimpses of what I can do in the [domestic T20 competition], but it was really pleasing to do it on the international stage," the South African-born left hander said.

Guptill had been first to the plate, his red hot bat plundering five sixes and six fours as he reached 63 off 25 balls before being the only wicket to fall at 95-1 in only the seventh over.

Hannah Peters Angelo Mathews plays another brilliant shot.

That allowed Munro to stride to the crease with the freedom to play his natural aggressive game. Few of the 17,058 in attendance, though, could have predicted what they were about to witness.

He smacked seven sixes and one four in his unbeaten 50 off 14 balls, the second fastest half-century in international Twenty20 history and the fastest for a New Zealand batsman.

India's Yuvraj Singh holds the world record, needing only 12 balls to go past 50 in 2007.

Kane Williamson's 32 not out off 21 seemed pedestrian in comparison, the Black Caps skipper getting the best seat in the house as Guptill and Munro found the middle of the bat with stunning regularity.

"Honestly, it was incredible," Williamson said.

"After the first [innings], I don't know what those two were thinking, but I thought it was going to be a bit of a scrap. They put up a total that could have been tricky had they took early wickets and took the pace off the ball.

"I'm not sure what those two had for breakfast, but it was certainly unbelievable to watch. We've seen Guppy do it all summer and to see Munners sort of outdo him was pretty special. It was world-class hitting."

A masterful 81 not out off just 49 balls from test captain Angelo Mathews rescued the visitors stuttering innings, easily the main contribution to their 142-8.

Mathews weathered the initial storm when he came in at 39-3, brilliantly increasing the tempo of his innings to finish with seven fours and four sixes.

Veteran opener Tillikaratne Dilshan made 28 in an action-packed 26-ball stay in an otherwise lack-lustre display after being sent in.

A key figure in the Black Caps three-run win in Mount Maunganui on Thursday, all-rounder Grant Elliott again played a crucial role with the ball.

Back at Eden Park for the first time since he belted South Africa's Dale Steyn for six to send New Zealand into the one-day World Cup final early last year, wiley medium-pacer Elliott returned figures of 4-22 to leave the Sri Lankan innings constantly battling for momentum.

Elliott found good support from Mitchell Santner through the middle, the young left-arm spinner taking 2-24 from his four overs.

While slightly expensive, quick-bowler Adam Milne also contributed to the visitors stuttering effort. Reaching speeds touching 150kmh, Milne took 2-36 from his four.

Mathews played superbly to try and help his side finish their tour on a high, but 60 balls later that possibility was swiftly swept aside.

There were 12 sixes and 10 fours between the three New Zealand batsman required, Munro clobbering another towering six over mid-wicket to seal victory.

After also making 36 off 26 in Thursday's win, Munro would likely need to perform very badly in the three upcoming T20s against Pakistan to miss out on making the squad for World T20, which starts in India on March 8.

New Zealand 147-1 (Martin Guptill 63, Colin Munro 50*, Kane Williamson 32*) Sri Lanka 142-8 (Angelo Mathews 81*, Tillikaratne Dilshan 28, Grant Elliott 4-22, Mitchell Santner 2-24, Adam Milne 2-36)

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* Sri Lanka cricket fans escorted from Eden Park by police

* Colin Munro hits Martin Guptill out of Black Cap record books with fastest 50

* Recap: Black Caps v Sri Lanka - T20 two