Pakistan skipper Inzamam-ul-Haq, in his fifth and final World Cup, was devastated by the defeat which could see him lose the captaincy of the side.
Mohammad Sami took three wickets, but Ireland triumphed
Unthinkably, the loss to Ireland put Pakistan out of the tournament.
"It was very disappointing," said the 37-year-old captain. "It wasn't easy to bat first but all credit to Ireland.
"They bowled tight lines and we played too many poor shots. It's my last World Cup, I wanted the team to do well but, sometimes, these things happen."
Coach Bob Woolmer, whose contract is unlikely to be renewed after the tournament, later said he was considering bowing out of international cricket.
He said: "I'm going to sleep on this one as I've had a very bad day, which ranks along with my worst days as a coach.
"Coaching is what I like to do but whether I continue to do that at international level is under discussion.
"I'm going to give it some thought."
Meanwhile, Pakistan were fined by the International Cricket Council for a slow over-rate during the match.
ICC match referee Chris Broad imposed the fines after Inzamam's side was ruled to be four overs short of its target at the end of the match when time allowances were taken into consideration.
Inzamam was fined 50% of his match fee and the rest of the team 20%