London Irish captain Bob Casey scored his first Test try on an afternoon of few highlights for Declan Kidney's Ireland side in Santa Clara, California.
The Grand Slam champions, missing a host of first-choice players due to the Lions tour and Leinster's Heineken Cup success, finished off their two-match tour of North America with an uninspiring 27-10 victory over the USA Eagles.
Casey barged over off a 13th-minute lineout maul to hand Ireland an early lead, which they boosted to 13-0 in first-half injury-time when new centre Ian Whitten finished off a breakaway attack.
But the US, who included six debutants in their starting line-up, were very keen to impress new coach Eddie O'Sullivan and they proved sticky opponents for an off-the-boil Ireland.
A lot of their good work was undone by a very poor place-kicking display from their number 10 Mike Hercus, who missed four kickable penalties.
Referee Chris White awarded the tourists a penalty try, 13 minutes into the second half, to almost put the game beyond the Americans' reach.
But, inspired by replacement out-half Ata Malifa, they launched a spirited fightback. Malifa dropped a goal and then set up centre Roland Suniula for a converted try.
With the gap down to 20-10 and both sides tiring, Ireland needed a final score to secure their second tour win and they got it when replacement scrum-half Eoin Reddan freed up tour captain Rory Best for a muscular burst to the line.
England Under-18 head coach John Fletcher insists his young side will be better for the experience after beating Italy in the bronze final to round out their 2015 Rugby Europe U18 Championship campaign in style.