The Black Caps, playing their 500th one-dayer and clearly inspired by Fleming's world record 194th match as captain, bowled out Pakistan for 223 after piling up 274-7 in the day-night international.
Fleming, who overtook Sri Lankan Arjuna Ranatunga's tally of 193 one-dayers as captain, led from the front with 80 and Scott Styris hit a fluent 86 after New Zealand were sent into bat.
Pakistan were struggling early in their run chase as they slumped to 83-4 in the 17th over.
But their hopes were resurrected by Mohammad Yousuf (71) and Shoaib Malik (52) who put on 94 for the fifth wicket.
The partnership moved Pakistan to a healthy 177-4 in the 37th over, needing 98 more from 82 balls, when pace spearhead Shane Bond swung the match New Zealand's way in his second spell.
Bond had Yousuf caught at cover by Fleming with his third delivery and then removed the dangerous Abdul Razzaq two overs later, hooking a catch to fine-leg after making six.
Bond finished with three for 45 from 10 overs while Kyle Mills and Jacob Oram picked up two wickets each.
After being sent in the 33-year-old Fleming opened the batting and stood his ground until the 38th over to steady the faltering innings.
The Black Caps were reduced to 23-2 before being rescued by a fourth-wicket stand of 108 between Fleming and Styris.
Styris, who needed a runner in the latter part of his innings due to a back strain, smashed 10 boundaries to lead a late batting assault.
Oram slammed 31 off 26 balls as New Zealand plundered 99 runs in the last 10 overs.
New Zealand ended the league with two wins from three matches, ensuring themselves one of the two semi-final spots from group B.
The winner of Friday's match here between Pakistan and South Africa will take the other berth as Sri Lanka, the fourth team in the group, head home empty-handed.
The race is also wide open in group A with three teams - world champions Australia, hosts India and the West Indies - in contention with one win each so far.