Houston - The United States rued missing out on a first win over Ireland before a record home crowd as the Irish prevailed 15-12 late on Saturday.
All the points came from penalties. Flyhalf Ian Madigan kicked over five and missed only his last one at the end, while US fullback Chris Wyles nailed all four of his chances.
Madigan punished US errors and a weaker scrum to run up a 12-6 half-time lead, and Ireland held on in the heat as the feisty Americans failed to finish off chances in front of a boisterous crowd of 20 181.
"It felt like we could have won that one," US wing Takudzwa Ngwenya said. "It felt like we gave them too much respect. At the end it came to bite us in the butts."
Madigan gave Ireland a 6-0 start with penalties from a scrum and ruck. Then the penalties followed a familiar pattern: The Americans gave away technical penalties for Madigan, and drew fouls for Wyles from pressure on the Ireland tryline.
At 12-6, Ireland should have put the game away in the 50th when Fergus McFadden broke through with support but fullback Robbie Henshaw, one of two debut starters, dropped the last pass.
Madigan's fifth penalty success came after US captain Todd Clever was sin-binned for a spear tackle on lock Devin Toner.
Wyles claimed his third penalty while Clever was away, and his fourth just after the captain returned to the field with about 15 minutes to go. But the scoring ended there.
"These are games that we're getting closer and closer in, and we need to win," Wyles said. "It's not just about competing for us. We want to win these games, and there's a bunch of guys in there who are bitterly disappointed."
Following Ireland's first win in five tests, first-time skipper Peter O'Mahony paid tribute to the five players who made their debut, three off the bench, and produced a win.
"The overall thing is we got a win away from home, it was a tough game, and we expected nothing less," O'Mahony said.
15 Chris Wyles, 14 Luke
Hume, 13 Seamus Kelly, 12 Andrew Suniula, 11 Takudzwa Ngwenya, 10 Toby
L'Estrange, 9 Mike Petri, 8 Todd Clever (captain), 7 Scott LaValla, 6 Samu Manoa, 5
Louis Stanfill, 4 Brian Doyle, 3 Eric Fry, 2 Chris Biller, 1 Shawn Pittman.
Substitutes: 16 Zach Fenoglio, 17 Nick
Wallace, 18 Phil Thiel, 19 Peter Dahl, 20 John Quill, 21 Robbie Shaw, 22 James
Paterson, 23 Adam Siddall.
15 Robbie Henshaw, 14 Fergus
McFadden, 13 Darren Cave, 12 Stuart Olding, 11 Simon Zebo, 10 Ian Madigan, 9
Isaac Boss, 8 Peter O'Mahony (captain), 7 Chris Henry, 6 Iain Henderson, 5 Devin
Toner, 4 Mike McCarthy, 3 Mike Ross, 2 Richardt Strauss, 1 David Kilcoyne.
Substitutes: 16 Mike Sherry, 17 Jamie
Hagan, 18 Tom Court, 19 Dan Tuohy, 20 Tommy O'Donnell, 21 Paul Marshall, 22
Paddy Jackson, 23 Felix Jones.