It's as tight as can be at the top of Group D with Serbia now in pole position for an automatic qualifying spot but either side can still top the group themselves if they are victorious and The Eagles slip up at home to Georgia, although on the evidence of the campaign so far that is fairly unlikely.
Ireland travel to Cardiff on Monday to face Wales in a FIFA World Cup qualifying match.
"Whatever game-plan we have, we are going to try to utilise it as best we possibly can", the Ireland boss said. We'll go and attack, go and score goals. That's the way it's set up.
"I will really have to think about it and replay the game again".
It should be a tense night for all involved tonight.
However, depending on how Croatia's game against Ukraine finishes, a draw may also see Wales drop out of contention for a play-off spot as the worst-placed runner-up.
The match will be under much scrutiny not only because of the high stakes.
David Meyler has promised the Republic of Ireland will give it "a hell of a go" as they attempt to leapfrog Wales and keep their World Cup hopes alive. We're one game away from maybe going to a play-off for the World Cup so we're delighted he's here.
Earlier, Wales secured a 1-0 victory in Georgia to remain right in the mix for a finals spot.
It was the Celtic striker's fourth goal in his last five Scotland games and had the "Tartan Army" of travelling fans believing in the dream of reaching the finals, being held in Russian Federation next year, for the first time in two decades.
"They were labelled this "golden" bunch of players before we qualified [for Euro 2016] and I fought against that, because they had not earned that tag".
Long missed three key chances in Friday's 2-0 victory over Moldova while his strike partner Daryl Murphy bagged a brace. The 3-1 loss to the reigning world champions means they are at +5 in goal difference on the runners-up table. One would not be enough but would still end Ireland's own play-off dream.
"We can win the match", he said. Serbia have booked a top-two finish - and a victory in their home game with Georgia will guarantee their place in Russian Federation.