The performance the national team has been waiting years for finally came to fruition at Aviva Stadium with a two-goal victory over the FIFA number five ranked side to keep the World Cup dream alive.
The pressure was on Heimir Hallgrimsson's side before a ball was even kicked following Hungary’s slender victory over Armenia, pushing four points clear of Ireland who knew that a defeat in Dublin would prove terminal regarding next summer’s tournament.
Portugal came looking for the win that would rubber stamp their place in the North American-hosted World Cup next summer, and it looked like they were well equipped to grind Ireland down as they took control of affairs from the kick-off.
All hands on deck for the home side, as they lined out in 5-4-1 formation, with every Portuguese pass and movement tracked, and yet the visitors looked to be making inroads with a few decent chances inside the opening 15 minutes.
Ireland’s answer came courtesy of a Caoimhín Kelleher kick-out, arrowed deep into enemy territory revealing the gameplan and showing this hard-working home side where the space existed and how it could be exploited.
Nothing from the first one, nor the second, but it woke the crowd from the hypnotic Portugal play and soon it had the 50-odd thousand believing that something special might happen.
Despite all the confidence ahead of the game, the talk of calculated risks and Portuguese weaknesses, no one inside the jam-packed arena could actually have predicted what was about to unfold.
First Troy Parrott almost catches the goalkeeper out, intercepting a clearance, then he nearly got cleaned out of it by the struggling stopper.
A corner would have to suffice, and the subsequent set-piece was executed to perfection.
Liam Scales was the target, arriving late to the back post; the header back across the face was textbook and Parrott found himself perfectly placed to nod home the opening goal.
Without much of a response from Portugal, Ireland continued with the gameplan, attempting to exploit that space, and sure enough, Chiedozie Ogbene almost punished that high line, racing through but ultimately watching his shot crash off the inside of the post.
The Portugal reaction finally arrived, and it was somehow matched by the resilient Ireland defensive unit, as wave after wave of penalty box action was thwarted, and with half-time approaching, Ireland were looking good to lead at the break.
Of course, they went one better, as Parrott again latched onto a ball over the top and calmly took on the defender before working his shot just inside the post.
The team would come out armoured with that two-goal lead and primed to sit in and suck it up for another 45 long minutes.
Fourteen minutes, in fact, as the game took another twist, and for the third consecutive home game the visitors were reduced to ten men.
Even more dramatic the fact that it was world superstar Ronaldo who would let the frustration get the better of him and lash out, catching Dara O’Shea with his elbow after a cross into the box was intercepted.
In truth, Ireland calmly coasted through the final 30 minutes and duly dealt with the late flurry to secure a famous victory and the most high-profile home win since the Germany victory ten years ago.
And yet, as the manager was quick to assert at the post match press conference, "it’s only half-time".
The World Cup dream is still alive, but there is a long, long way to go to have a chance of making it to the top table for the first time since 2002, and it all continues in Budapest on Sunday where Ireland still need to win to secure second place.
"First, it's OK to smile and enjoy this win, but it's just half-time," said Hallgrimsson.
"We wanted to go for the last game and still have a chance, and we have that now.
"So what a moment for us, even talking after the game against Armenia, when things didn't look well, to have this chance now.
"It's in our hands to qualify for the next round, and after this performance, I think there's a lot of positivity in that performance we did, but now we just need to get all the energy back.
"That's the prime focus now, is to regain as much energy as we can for that second game in Hungary."
A bemused manager spoke about the margins that decide games as he likened the winning performance at Lansdowne Road to the heartbreaking loss in Lisbon.
"Margins in football, looking at them (Hungary) playing Armenia, and Armenia had two golden chances, and in the last kick of the game he misses the ball in front of goal.
"You can see how little and how marginal this is at this level, winning or losing, being a hero or being a villain.
"That's the name of the game, and we are judged by performance and wins."
Hallgrimsson was asked about Evan Ferguson’s chances of making it onto the plane to Budapest having missed the Portugal game through injury.
And while the manager said that they would enquire as to his wellbeing, he hinted that he might plan without the striker if there are any doubts.
"He trained yesterday, and he should have trained today, so we'll know more tomorrow," said Hallgrimsson.
"Where he is in his fitness, he's never going to be 100%, but if he is close to, we just don't know.
"We'll have more info tomorrow. But given that, we didn't lose any player on a yellow card, because we had quite a few on a yellow card that could have been suspended in Hungary, and nobody got seriously injured…
"So I don't know if we would take the risk if he is doubtful, but we're definitely going to check and see if he is available."
Watch Hungary v Republic of Ireland in World Cup qualifying on Sunday from 1.30pm on RTÉ2 and the RTÉ Player. Follow a live blog on the RTÉ News App and on rte.ie/sport. Listen to live commentary on RTÉ Radio 1.
