Before rating their chances of making it that far, here's how they work.
Wales and Republic of Ireland know the importance of this clash and will both be desperate for the three points that could see them into the play-offs. The big centre-forward has given O'Neill a selected headache for upcoming encounters once the Ireland manager has all of his attacking available.
"We haven't been sat with pen and paper, but we're aware of scores elsewhere", Wales defender Gunter said. They do have a route to the play-offs involving a draw but that's only if the Group I game between Ukraine and Croatia in Kiev finishes level and doesn't have more goals in it than the match in Cardiff.
"But, even before what happened, it was a physical game and we expected it to be". Even without Gareth Bale, Wales will present a formidable challenge - but at least we no longer need favours from elsewhere to help us get the job done. That didn't look too likely given how poor the Georgians were against Wales on Friday, but then that was also down to how good Coleman's side were. Wales is ranked second in Group D, a point behind group leaders Serbia, while Georgia is fifth with five points.
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The Green Wave (3-2, 1-1 American) blistered Tulsa, 62-28, scoring its most points in a conference game since 1997. Oklahoma has a rough schedule ahead, facing Texas, Kansas State, Texas Tech and Oklahoma State in the next month.
Tom Lawrence's early second-half strike was enough for Wales to secure a crucial 1-0 win over Georgia.
Celtic cousins separated by the Irish Sea, Wales and Ireland are more accustomed to facing off on the rugby pitch and have never previously tackled each other in a football match of such magnitude. "I don't think it's lost its lustre at all". A draw in Belgrade would leave them at the mercy of a Wales win against the Republic.
The Republic of Ireland boss is, meanwhile, boosted by the return of Robbie Brady and James McClean, both of whom served their respective one-match bans against Moldova.
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'We have found it hard scoring goals, it's been a problem since I came in.
As for the table to determine the eight best-placed second place teams (which discounts result against the side finishing bottom) and thus who plays in the play-offs, Wales are now ahead only of Croatia, and only be virtue of having scored one more goal.
Prior to the game, all eyes were on Wales playing in Georgia.
Having received an abject apology from the Georgian FA after what was described as a technical fault led to their anthem being cut short in Tbilisi on Friday evening, Wales have taken the idea on board and announced they will be doing something similar in Cardiff.
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