Ireland seemingly had control of yesterday's opening Vodafone Ireland WXV Series clash when Erin King touched down just six minutes into the second half.
The captain's sixth try in 13 Tests saw the girls in green take a 31-12 lead, but their own indiscipline, coupled with the powerful USA pack coming to the fore, saw them succumb to a 40-36 defeat.
The Women's Eagles showed a ruthless streak when crossing for three converted tries while Vicky Elmes Kinlan was in the sin bin, and Vodafone player-of-the-match Freda Tafuna's 72nd-minute effort had them out of Ireland's reach.
Buy Your Tickets For Ireland v Japan
It is a setback for Scott Bemand's side at the start of a new international season, but their execution in attack during the opening half-an-hour certainly bodes well for the rest of this autumn block.
Giving her reaction to the surprise result at Tallaght Stadium, King said: "It's disappointing. We came out of the blocks and we showed what we're capable of. We're frustrated that we didn't show that for 80 minutes.
"You know, it's our first game of the season, and we were definitely looking to hit the ground running and we know what we're capable of.
"So, yeah, lots of learnings, and we say that you get your best learnings from your losses probably. If we can take them and bring them into next week against Japan, we'll be happy with that."
The visit of 11th-ranked Japan to Connacht's Dexcom Stadium next Sunday (kick-off 12.45pm) offers King and her team-mates an immediate opportunity to get back to winning ways on home soil.
They will take a lot of encouragement from their fast start against the USA, with tries from Elmes Kinlan, Clíodhna Moloney-MacDonald, and Aoife Wafer on the board inside the opening 17 minutes.
Moloney-MacDonald brilliantly combined with Stacey Flood, off the side of a midfield ruck, to split open the American defence for the first try, as the hooker's inside pass did the damage.
Strong forward play paved the way for the next two scores, and an excellent run down the left wing from replacement Anna McGann played in Eve Higgins to bring the Irish try haul to four.
Debutant Jemima Adams Verling also had some good moments, as the hosts displayed a clinical edge - they ended the opening 40 minutes averaging four points per attacking 22-metre entry, and with eight line breaks and 25 defenders beaten, 98.5% rucks won, and 259 post-contact metres.
However, the US team flipped the script on the hour mark and punished a series of Irish penalties, making big metres with their maul as the home defence struggled and conceded 28 points in a devastating 15-minute spell.
Reflecting on two contrasting halves, King commented: "The USA are a big, strong, powerful team, and we're probably a bit quicker. In the first half we played to our strengths, going out wide, getting the ball to the wingers.
"But probably just our discipline slipped a little bit, and that gave them some easy 'ins'. We'll come back stronger from this, and it was a positive day for Jemima who got her first cap.
"Delighted with that, and a few girls got on the scoresheet there, so yeah, definitely loads of positives but a lot of learnings, and we're probably a little bit frustrated.
"We have so much potential in our squad. I love playing with this team, we have so much talent, and it's a joy to get to captain this team.
"I think the girls show day in and day out what they're capable of, so we'll be a little bit frustrated but I have no doubt that we're going to come together and come back stronger as a team."
The 22-year-old back rower led the tackle statistics for Ireland, landing 19 hits for a 90.9% success rate. She made one line break, beat two defenders, and totalled 23.5 metres from seven carries.
From a squad perspective, there were just too many errors when the pressure came on in that second period, with some cheap penalties allowing the American maul and power game to dictate the outcome.
Head coach Bemand spoke afterwards about how his charges have got to be 'cuter in terms of how we stop the opposition's momentum and arrest it and get back on top'.
Giving her assessment, King added: "They got the momentum there and they kept the momentum, and it's probably something that we need to look back on and take the learnings from that.
"If we're going to get anything out of that game, it is going to be the learnings and definitely try to shift that momentum.
"We showed in the first half what we can do. And just probably play to our strengths a little bit more and not letting it play into their hands.
"But yeah, like I said, loads of learnings from that, and we'll come away from that and go again, regroup together and go again next week."
