The winner will advance to the quarterfinals and a match against four-time champion Australia next Friday, again at the Adelaide Oval.
Pakistan made two changes, with Mohammad Irfan (injured) and Younis Khan out, replaced by Haris Sohail and Ehsan Adil.
There were no changes to the Ireland starting lineup.
The forecast was for mostly sunny skies and very little chance of rain that could affect the outcome.
Both teams have three wins each so far in the tournament. Pakistan, the 1992 champion, has not won a match when batting second at this World Cup.
Related story
Nepal loses toss, Bibek and Anil on bench
