Zaheer leads India to easy win
Both teams had already qualified for the second round of the tournament.
Left-arm swing bowler Zaheer helped restrict Ireland to just 112 for eight after the match was was reduced to 18-overs a side following a rain delay.
Man-of-the-match Zaheer was well supported by spinner Pragyan Ojha, who completed figures of two for 18 from four overs.
Rohit Sharma (52 not out) and Gautam Gambhir (37) put on 77 for the first wicket for defending champions India who reached 113 for two with 15 deliveries remaining under the Trent Bridge floodlights.