At the end of a totally uninspiring first half Ireland led 13-6 against an opposition that would struggle in the Celtic League.
David Humphreys opened the scoring with a 7th minute penalty but Mike Hercus levelled with his second effort ten minutes later.
Ireland's first try arrived courtesy of Eric Miller in the 24th minute and they should have had a second in the 35th but captain Brian O'Driscoll threw his pass behind the flying Shane Horgan.
Within 15 minutes of the restart two Geordan Murphy tries added respectability to the scoreboard before Tommy Bowe marked his senior international debut with a try that owed much to Donncha O'Callaghan's take off the top of a line-out and O'Driscoll's off-load in the tackle.
After that a tiring USA did well to restrict Ireland to just three tries, the final one coming from replacement Peter Stringer in the 80th minute.