Zaman smashed 24 boundaries and five sixes in a blistering innings and went on to become the sixth international batsman to score a double hundred in the 50-overs format.
Up against a weak Zimbabwe attack, openers Imam-ul-Haq and Zaman adopted a ruthless approach to record the first 300-run opening stand in ODIs.
The record for the highest opening partnership was earlier held by Sri Lanka's Upul Tharanga and Sanath Jayasuriya, who had added 286 against England at Leeds in July 2006.
Ul-Haq blazed away to 113 off 122 balls, studded with eight fours, before falling to spinner Wellington Masakadza.
Asif Ali joined Zaman to build an unbeaten 95 run partnership as they finished with 399 for 1 at the end of the innings.
Earlier in the day, Pakistan skipper Sarfaraz Ahmed won the toss and opted to bat in the fourth ODI. The visitors have dominated the series, bowling Zimbabwe out for 67 on Wednesday to clinch an unassailable 3-0 lead.
(Reporting by Hardik Vyas in Bengaluru; Editing by Christian Radnedge)
