Republic of Ireland's Nations League misery continued as Eduard Spertsyan blasted Armenia to victory in Yerevan.
The midfielder hammered a long-range 75th-minute effort past 'keeper Caoimhin Kelleher, making his competitive debut for Ireland, to hand the League B newcomers victory and revenge for their controversial Euro 2012 qualifier defeat in Dublin.
Stephen Kenny's men, who have now not won in 11 attempts since the competition was introduced, could have few complaints on a night when their eight-game unbeaten run came to a disappointing end at a sweltering Republican Stadium.
Ireland enjoyed the upper hand for long periods, but failed to convert dominance into chances.
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Callum Robinson had a mishit first-half shot cleared off the line and Chiedozie Ogbene headed over when he might have done better, but they wilted after the break and were caught by a sucker punch, albeit one delivered with aplomb.
Shane Duffy had to block Spertsyan's shot at full stretch seconds later and the defender picked up a ninth-minute booking for an untidy challenge on Barseghyan.
Ireland threatened for the first time when Josh Cullen fed Ogbene and he slid the ball into Robinson's path, but the striker could only ripple the side-netting with his attempt.
Neither side was able to exert any measure of control in an error-strewn passage of play and Robinson might have done better when he scuffed Ogbene's 16th-minute cross towards goal, where Hovhannes Hambardzumyan cleared off the line.
Duffy headed over from Cullen's corner with the visitors having regained their composure, but clear-cut openings proved few and far between.
Armenia keeper David Yurchenko caused panic in his own penalty area with a less than effective punch as he attempted to deal with Troy Parrott's driven cross and Spertsyan survived penalty appeals for handball as Coleman recycled.
Ogbene dragged a 38th-minute shot past the far post after Robinson had collected Hendrick's fine pass and squared before Parrott curled wide from distance four minutes before the break with Ireland pressing.
However, Ogbene passed up perhaps the best chance of the half in stoppage time when he was left unmarked from Cullen's free-kick, but powered his header inches over.
The home side served warning of the threat they posed on the break within five minutes of the restart when Barseghyan played Hambardzumyan into space down the right and then collected his return pass before stepping neatly inside Parrott to curl a superb shot into the top corner.
However, the celebrations at the Republican Stadium stopped almost as soon as they had begun as an offside flag spared Kenny's side and Barseghyan could not find the same accuracy with a similar effort from greater range six minutes later.
Duffy headed a 62nd-minute Cullen corner straight at Yurchenko and put another attempt wide from Stevens' cross seconds later as the visitors responded.
Hendrick curled a 69th-minute shot into Yurchenko's midriff, but it was Armenia who took the lead with 15 minutes left on the clock when Spertsyan was allowed to close in on goal before unleashing a 25-yard strike which beat Kelleher's despairing dive and went in off the upright.
John Egan thumped a later header wide as the Republic sought salvation but Armenia, who lost 9-0 in Norway last time out, held firm to take the points.
Stephen Kenny admitted the Republic of Ireland had only themselves to blame after slipping to defeat.
He said: "Obviously we lost the game, a tight game really overall. It's not a game that we deserved to lose, you couldn't say that on the balance of play or the balance of chances, but we've lost it and we've only got ourselves to blame, so we are disappointed.
"I felt the last 20-25 minutes of the first half, we were really in control, but we didn't start the second half like that at all. I was disappointed that we didn't start the second half like we ended the first.
"We seemed to be susceptible to counter-attacks and we found it difficult to break them down. We created some good chances but we didn't take them, some half-chances, but they didn't really have any chances bar the offside goal, so it was disappointing overall."
Kenny's side must regroup quickly with Ukraine and Scotland due to arrive in Dublin for the second and third instalments of this month's quadruple-header, although the defeat in Yerevan was perhaps their most disappointing result since they were beaten 1-0 at home by Luxembourg in March last year.
Asked about his challenge to his players to win the group, he said: "We've made life difficult for ourselves, but rather than focusing on that, we've got to focus on bouncing back on Wednesday.
"We've got two home games now, we need to dust ourselves down. We're disappointed with ourselves, we know it's a poor result, we're well aware of that."
Armenia coach Joaquin Caparros was delighted with the way his side adopted a new approach after the break and were eventually rewarded.
He said: "I am very pleased with the way we played in the second half. I have to praise my players because it's a very good result for our team.
"In the first half, they had a lot of possession of the ball but they didn't have any opportunities apart from the very end, the header which went wide.
"We got more confidence and had more possession. We worked really hard and earned our luck with the goal.
"It's one of the greatest victories of the Armenian football team because Ireland is a very good team."
Asked if he felt Kenny had disrespected Armenia by talking about winning the group during the build-up, Caparros added: "It's an opinion and it's a way to motivate your own team.
"Football is only about the result. We don't have to argue about anything because it's only about the result."
- Armenia secured their first win against Republic of Ireland at the third attempt of trying, following defeats in September 2010 (1-0) and October 2011 (2-1).
- Republic of Ireland suffered their first defeat in any competition since last September against Portugal in a World Cup qualifier, ending their eight-game unbeaten run.
- Republic of Ireland have failed to win any of their 11 UEFA Nations League matches (D5 L6), while only San Marino (0) have netted fewer goals than the Boys in Green (2) in the competition's history.
- Armenia have won seven of their 13 games in the UEFA Nations League (D3 L3), finding the back of the net in 11 of their 13 games in the competition (24).
- Eduard Spertsyan scored his second ever goal for Armenia and his first since his debut in March 2021 vs Romania.
- James McClean (91) came on to become the 10th different player to make over 90 appearances for Republic of Ireland, having made his international debut back in February 2012.
Republic of Ireland host Ukraine in the Nations League Group B1 on Wednesday June 8 at the Aviva Stadium; kick-off 7.45pm.
With skipper Seamus Coleman and Enda Stevens operating as wing-backs, Ireland went straight on to the offensive in an effort to seize the initiative, but it was Kelleher, playing in place of the injured Gavin Bazunu, who was called upon to keep out Tigran Barseghyan's skidding sixth-minute effort after Nathan Collins had surrendered the ball.