New Zealand players celebrate the wicket of Pakistan's Iftikhar Ahmed during the T20 in Hamilton on Sunday. AP

New Zealand overcame the loss of its captain in an innings that faltered late to beat Pakistan by 21 runs in the second Twenty20 international Sunday, taking a 2-0 lead in the five-match series.

The Black Caps failed to build on the foundation of the first half of its innings, making 194-8 batting first after being 111-1 at the end of 10 overs. The batting slump followed captain Kane Williamson retiring hurt after 10 overs with a tight hamstring.

Pakistan also stumbled in the second half of its innings and was bowled out for 173 in the 20th over.

Williamson is making a managed return from a serious knee injury and New Zealand would fear any setback to his rehabilitation. But while he didn’t field, Williamson was still padded up and apparently prepared to bat at the end of the New Zealand innings.

Finn Allen’s 74 from 41 balls set a cracking pace early on in the New Zealand innings. Allen put on 59 in 5.1 overs with Devon Conway (20) for the first wicket and 52 in 4.9 overs with Williamson before the Kiwi captain retired hurt on 26.

The innings began to falter at that point and New Zealand lost 3-35 between the 11th and 16th overs. Allen was out at 137-2, then Daryl Mitchell fell at 147 and Mark Chapman followed at 157 as the innings began to trend sharply downwards.

Mitchell Santner made a bright 25 before being wastefully run out as New Zealand lost its last seven wickets for 55 runs.

Aamer Jamal (right) of Pakistan is stumped by New Zealand's Devon Conway during the T20 in Hamilton. AP

"It was a good surface which we’ve come to expect here at Sedden Park and the way Finn Allen and the boys at the top set it up was very pleasing,” New Zealand’s stand-in captain Tim Southee said. "But Pakistan pulled it back well and the two innings were quite similar in a way.”

New Zealand was relieved Pakistan also produced an innings of two halves. It looked well on course to level the series when Babar Azam and Fakhar Zaman made half centuries in an 87-run partnership for the third wicket.

Fakhar reached his half century from 23 balls with three fours and five sixes and seemed likely to follow Allen in providing the impetus for a substantial innings. But he was out at that score and the onus once again fell on Babar to guide Pakistan home.

He made 57 and was the anchor of Pakistan’s innings in the first international at Auckland on Friday when the tourists fell 46 runs short in a demanding run chase.

Babar followed his 31st T20 international half century with his 32nd Sunday, again as the bulwark of the Pakistan batting.

But he fell for 66 to the first ball of the 18th over when Pakistan was 153-5, needing 42 from the last 18 balls.

He was out to the bowling of speedster Ben Sears as he was in the first match and his dismissal again heralded the beginning of the end for Pakistan.

Sears, Adam Milne and Southee helped New Zealand put the brakes on Pakistan at the end of its innings. Milne took 4-33, Sears 2-28, Southee 2-31 and Ish Sodhi took 2-33 after conceding 19 runs from his first over.

"Milne was outstanding with the ball and Sears is a young guy who shows a lot of character at this level,” Southee said. "I think Ish Sodhi shouldn’t be overlooked in his effort to come back and get two vital wickets for us.”

Associated Press