Many Irish eyes were fixed on Switzerland's clash with Georgia on Friday night, but it was Sweden's defeat of Romania at the same time that had the most immediate impact on Mick McCarthy's men.
The Swiss squeezed past Georgia 1-0 in St Gallen thanks to Cedric Itten's 77th-minute header.
Had the Georgians held on for a draw, the Republic of Ireland would have needed to beat Denmark by two goals on Monday night to seal automatic qualification - providing Switzerland beat Gibraltar in their final game.
Now, the mission is a little more straightforward: a win of any description against Age Hareide's Danes will send Ireland to the Euros.
If the Boys in Green fall short, however, they are now guaranteed the safety net of the play-offs.
Sweden's 2-0 win Bucharest sealed their ticket to the finals and also ensured there is now no scenario in which Ireland will not go into the March play-offs should they fail to beat Denmark.
They will face a standalone semi-final - most likely away from home based on their current ranking - and then a final to get there.
Northern Ireland are also heading for the play-offs after a stalemate with the Netherlands on Saturday night ended their hopes of automatic qualification from Group C.
Group E is likely to decide which team Ireland will play. Slovakia, Bosnia and Herzegovina and Wales are the sides in contention to play Mick McCarthy's side for a place in the play-off final, but it is a complicated formula.
The draw for the play-offs takes place at UEFA headquarters in Nyon on Friday.
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