Christian Eriksen's treble breaks Ireland's hearts and sends Denmark to Russia
Christian Eriksen plundered a stunning hat-trick as Denmark shot the Republic of Ireland's World Cup dreams down in flames to book their ticket to Russia in emphatic style.
The Tottenham midfielder, who had been effectively shackled in Copenhagen on Saturday evening, took the second leg of the play-off tie by the scruff of the neck with two superb finishes either side of half-time before lashing home a third late on.
In the process, he took his tally for the campaign to 11 goals, just two fewer than the Republic managed in their 12 games in the competition, before substitute Nicklas Bendtner converted a last-minute penalty.
His assertion proved astute as despite taking an early lead through Shane Duffy's header, Ireland were simply unable to find the right balance between attack and defence after Cyrus Christie's own goal had restored parity.
The organisation which had characterised the Republic progression to the play-offs disintegrated horribly and in the end, they were picked off in ruthless fashion.
Having spent the 90 minutes in Copenhagen largely defending for dear life, there was an acceptance that they would have to be far more proactive if they were going to get past the Danes.
It was no surprise when O'Neill once against ignored the clamour for 34-year-old Wes Hoolahan's inclusion, and he could hardly have been more delighted when, with less than six minutes played, his team took the lead.
Robbie Brady's set-piece delivery has at times left something to be desired during the current campaign, but the free-kick he floated into the Danish penalty area caused panic and when striker Nicolai Jorgensen could only help the ball towards his own goal, Duffy rose to head past advancing goalkeeper Kasper Schmeichel.
However, that was never likely to be decisive and had it not been for keeper Darren Randolph, who reprised his heroics in Denmark with good saves from William Kvist and Pione Sisto in quick succession, the visitors would have been back in it.
Ireland might have increased their lead with Daryl Murphy and James McClean going close, but the wheels came off in spectacular fashion inside three devastating minutes.
Christie was desperately unfortunate to turn the ball into his own net after Andreas Christensen's stabbed 29th-minute shot had come back off the post and hit him, but Harry Arter might have done better to prevent Sisto getting in the cross which handed the Chelsea defender his opportunity.
The dust had barely settled when an Irish error was punished once again, Yussuf Poulsen robbing Stephen Ward before twice exchanging passes with Jorgensen, who teed up Eriksen to sweep a first-time shot past Randolph and in off the underside of the crossbar.
The Danes revelled in the extra freedom that afforded them and Randolph had to parry a well-struck Sisto effort after Eriksen had turned neatly to send him sprinting towards goal.
Play switched rapidly from end to end with Duffy planting a firm header straight into Schmeichel's arms before Eriksen ran half the length of the pitch unopposed only to see his shot blocked by the diving Randolph.
However, the Middlesbrough keeper was exposed once again with 63 minutes gone as Eriksen effectively killed Irish hopes for good, receiving Sisto's pass and expertly curling a left-foot shot inside the far post to make it 3-1.
He completed his hat-trick by dispatching a rasping drive into the roof of the net as Ward faltered once again, and there was still time for Bendtner to have his say when he converted a last-minute penalty after being felled by Duffy.