The 16-year-old, who made his County debut against New Zealand A last summer, scored a run-a-ball 88 and shared a fourth-wicket partnership of 150 with Middlesex’s Martin Andersson as England posted 225-9 in their 50 overs.
Pakistan, who had won the first two games of the series, were then bowled out for 155 to give the England Development Programme side a good win.
“Victory represents the hard work that all of the players have put in since arriving out here,” said head coach Iain Brunnschweiler.
“They have continued to adapt to the conditions and become more and more consistent in their delivery of their skills.
“Saif Zaib and Martin Andersson’s partnership was absolutely superb.
“Both players knew it was going to be tough up front and they needed to play strong shots in order to get in, whilst still being positive.
“Once they had done the hard work, they both played intelligently and expanded their scoring options accordingly.
“Their platform set up an excellent total of 225, which I was really pleased with.”
The EDP squad complete their tour with a three-day match against Pakistan which starts on Tuesday.