Veteran left-arm spinner Daniel Vettori(4/18) and pacer Trent Boult (3/34) had reduced Afghanistan to 59/6 in 20th over. However, Samiullah Shenwari (54) and Najibullah Zadran (56) forged an 86-run partnership for the seventh wicket to bail the team out of the slump. Yet they were bowled out for 186 in 47.4 overs.
In pursuit of an easy target, the host hardly broke a sweat and got over the line with ease in 37th over. Skipper Brendon McCullum raced to a 19-ball 42 to provide a sparkling start.
After he lost his wicket to his Afghanistan counterpart Mohammad Nabi, Martin Guptill (57) was joined in middle by in-form Kane Williamson (33). They stitched a 58-run stand before young Williamson was caught by Shenwari at mid-wicket off pacer Shapoor Zadran.
Guptill, 28, registered his 22nd One-Day International (ODI) fifty.
Later, experienced Ross Taylor (not out 24), Grant Eliott (19) and Corey Anderson (not out 7) completed formalities to give the co-host their fifth win in as many matches. They are on top of Pool A, while the Afghans are sixth with one win in five matches.
New Zealand are expected to make it six out of six as they will face Bangladesh on March 13. Afghanistan, who are already out of race for the quarterfinals, will have to battle it out against England for their second win.
Earlier, Afghanistan innings got off to a poor start with two openers Javed Ahmadi(1) and Usman Ghani (0) perishing to pacer Boult and Vettori.
From 6/2 in the third over, they stooped to 59/6 in 20th over. Asghar Stanikzai (9) lost his wicket to left-armer Boult. Vettori dismissed in-form Nawroz Mangal (27), Nabi (6) and wicket-keeper-batsman Afsar Zafai (0) as the cup debutants stumbled to 59/6.
Afterwards, a seventh-wicket partnership between Shenwari (54)and Najibullah (56) for 86 runs rescued them. Their stand became the fifth highest for the seventh wicket in the history of the quadrennial event.
The 22-year-old left-hander Najibullah recorded his second ODI half-century. He hit eight fours and two sixes before offering a catch to Vettori at third man off pacer Adam Milne.
For 28-year-old Shenwari, it was his 10th fifty and second in the tournament. He had scored 96 in a winning cause against Scotland. On Sunday, the right-hander played it slow and during his 110-ball knock, he hit five fours and a six.
Shenwari offered a simple catch to Ross Taylor and square leg off medium pacer Anderson, who ended the Afghanistan innings by taking the wicket of Hamid Hassan (16). They were bowled out for 186 which was not at all a task for the strong batting line-up of New Zealand.