The US Eagles were denied a famous first victory over Ireland in Houston as the tourists escaped Texas with a 15-12 win in front of new coach Joe Schmidt.
Mike Tolkin's team just ran out of steam against a callow Irish side who were left hanging on to their three-point lead in an edgy second half.
Fly-half Ian Madigan kicked all of the visitors' points in front of 20,181 at the BBVA Compass Stadium, a record for a United States home game, while Saracens' Chris Wyles scored all of his side's 12 points.
Ireland were starting with a number of new faces, but they began well with new cap Robbie Henshaw making two big hits early on and Madigan scoring his first international points with a ninth-minute penalty after Mike Ross got the nudge on his opposite number Shawn Pittman at scrum-time.
It was to prove a trend as the Eagles' front-row just couldn't handle the Irish trio of Dave Kilcoyne, Richardt Strauss and Ross and they forced another penalty minutes later for Madigan to double his tally.
The new out-half was looking sharp and moving the ball wide, but after one of his long, drifted passes things almost went drastically wrong for Ireland as Darren Cave was isolated and from turnover ball Luke Hume chipped over the cover.
The ball evaded the onrushing Henshaw, allowing Hume to rush towards the line until he was tackled by Ireland's other debutant, Stuart Olding.
The Eagles picked and drove and, while Wyles did have an unsuccessful cut for the line, the referee had his arm up and the Saracens full-back got his side off the mark.
While their scrum was dominant, Ireland's lineout was malfunctioning but it was from a rare success that Madigan was handed his third opportunity and he took it gladly to make it 9-3.
But Ireland could not pull away and Samu Manoa, who had earlier emptied Ireland captain Peter O'Mahony (pictured) in a huge tackle, broke through the Irish cover and the scrambling defence conceded a penalty for Wyles to score.
The scrum provided one more chance for Madigan to make it 12-6 at the break, but with the temperatures continuing to hover in the mid 20s there was concern over Ireland's ability to endure even with the additional water breaks.
Buoyed by being so close, captain Todd Clever got the US on the front foot from the off after the break and he burst through a Kilcoyne tackle early on and only an excellent turnover from Chris Henry and Peter O'Mahony saved the visitors.
A Manoa mistake from a Wyles knock-on allowed Madigan make Ireland's total 15 and it should have been more when Fergus McFadden scythed through on an Isaac Boss pass, only for Henshaw to spill his pass with the line at his mercy.
They almost regretted it. Despite losing Clever for 10 minutes after his tip-tackle on Devin Toner, the US got on top and, roared on by the boisterous crowd, Wyles closed the gap to six points after Henshaw failed to deal with a Manoa chip, putting his defence under pressure, before another ruck infringement allowed him make it a three-point game.
But Ireland weathered the storm as they emptied their bench and US coach Tolkin persevered with the majority of his starting XV.
Taku Ngwenya had one opportunity to show his pace in the closing stages, but replacement Felix Jones hauled him down and the American winger was penalised for holding on.
Madigan missed his kick, but used up precious seconds and when Toner rose highest to claim the restart, Ireland wound the clock down and Paul Marshall cleared to touch to break local hearts.