Following the high of last week's triumph over New Zealand, the visit of the Americans was a slightly anti-climactic way for an Irish side to end 2018 with their 11th win in 12 internationals.
But the open, scrappy encounter was still a significant game for an almost entirely new-look home side as wing Andrew Conway stood out with a hat-trick of tries while Jack Conan and Rhys Ruddock showed off Ireland's plethora of back row options.
Ruddock and Conway combined for the opening try in the third minute as the Munster winger danced his way into space just inside his own half before exchanging passes with Ireland's captain for the day and touching down.
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Conway had his second try within 15 minutes but only after the United States' big, free-scoring hooker Joe Taufete'e took advantage of some dreadful Irish defending to add to the two tries he scored in the Eagles' 30-29 win over Scotland in June.
The spirited visitors, ranked 13th in the world, threatened to make a game of it by levelling things up again at 14-all, this time with a well-earned penalty try, and left Ireland needing a try from number 8 Conan to go into halftime with a 10-point lead.
However they were far more controlled in the second half as the U.S. scrum struggled to cope with the loss of Taufete'e to injury, allowing Stuart McCloskey and Quinn Roux to help themselves to their first international tries after Tadhg Beirne opened the floodgates.
By ensuring all 43 players who joined camp last month got some game time, coach Joe Schmidt was able to give centre Sam Arnold a debut off the bench, hand John Cooney a first start at scrumhalf and watch Will Addison add stints at fullback and wing to a portfolio that also included a start at centre.
All that was left was for Conway to breeze in for his hat-trick after fantastic work from the only survivor of last week's 16-9 win, Garry Ringrose, and for John Ryan to complete the scoring with his own first try for his country.
(The story was corrected to show Tadhg Beirne's try not his first for Ireland)
(Reporting by Padraic Halpin; editing by Tony Lawrence)
