Cardiff Blues winger Alex Cuthbert scored two tries as the Barbarians beat Ireland by one point for a third time in recent years.
The invitational side's other try at Thomond Park came from Leinster's South African back Zane Kirchner.
The three Irish tries came from Ulster players Craig Gilroy, Chris Henry and replacement Paddy Jackson.
Back row Henry, 30, was playing his first match in an Ireland shirt since undergoing heart surgery last year.
Jackson's try came in the final minute with Ian Madigan drop-kicking the conversion from the touchline.
It meant another one-point game as the Barbarians had beaten Ireland 29-28 three years ago and 31-30 in 2000.
The first half did not witness much of the flamboyant, open and attacking play with which the Barbarians are associated.
But it was a competitive affair on a damp, uninviting night in Limerick.