Wales are hoping to snatch the final automatic qualifying berth for Euro 2020 as they take on Hungary on Tuesday, after the Republic of Ireland were left to settle for a crack at reaching the finals via the play-offs.
Ryan Giggs's Wales side, who have already qualified for the play-offs should things not go their way, face Hungary in Cardiff knowing a victory will guarantee them a place at next year's 24-team tournament and a chance to repeat their fairytale run to the semi-finals in France in 2016.
Despite the presence of Gareth Bale and Aaron Ramsey in their ranks, Wales have not often convinced in this qualifying campaign but a 2-0 victory away in Azerbaijan on Saturday set up this winner-takes-all showdown.
"We have got that momentum. I think we'll have to be better than we were the other night if we are going to win," warned Giggs.
"But I believe in the players. I believe in the group that we've got and the qualities they possess."
Wales are currently third in Group E, a point behind second-placed Hungary, while 2018 World Cup runners-up Croatia have already secured top spot.
It is not quite a straight shoot-out between Tuesday's opponents in Cardiff though -- if the game ends in a draw, Slovakia can leapfrog them both by defeating Azerbaijan.
For whoever misses out on automatic qualification, there will however be a second chance to qualify via the play-offs.
That is the path Ireland will have to take if they are to reach the finals after a 1-1 draw with Denmark in Dublin on Monday saw them finish third in Group D behind Switzerland and the Danes.
"Overall I'm very pleased with the performance and very proud of the players, particularly after conceding, to push them right to the limit," Ireland manager Mick McCarthy told Sky Sports after the game.
"Play like that in the play-offs and we can beat anybody."
Nineteen of the 20 automatic qualifying berths for the Euros have now been allocated.
- Second chance -
The remaining four spots will go to the winners of the play-offs which will take place in March -- the draw for those ties will be on Friday at 1100 GMT.
The draw for the final tournament will take place in Bucharest on Saturday, November 30.
The seemingly highly confusing play-off format is based on the final standings in the inaugural UEFA Nations League, which split European nations into four divisions and offered teams from each tier a second chance to qualify for the Euros.
Georgia, Belarus, North Macedonia and Kosovo will meet in the play-offs in the bottom tier League D, with the winner after two semi-finals and a one-off final advancing to a first ever major tournament.
Scotland -- who finish their disappointing qualifying campaign against Kazakhstan on Tuesday -- already know they will have a home play-off on March 26.
If they win that, Steve Clarke's team will advance to a final against either Norway or Serbia for the chance to reach a first tournament since the 1998 World Cup.
Northern Ireland and the Republic of Ireland will only get an idea who they might face in the play-offs after Tuesday's games.
As for the draw for the finals themselves, England already know they will be in the first pot of seeds alongside the likes of Italy, Belgium and Spain, who have just reappointed Luis Enrique as coach.
However, France and Germany could yet both end up in the second pot of seeds for a competition to be staged in 12 cities across 12 different nations between June 12 and July 12 next year, with the semi-finals and final at Wembley.
Gareth Bale and Wales know a win over Hungary on Tuesday will see them qualify for Euro 2020
The Republic of Ireland will have to go through the play-offs to qualify for Euro 2020 despite Matt Doherty's late equaliser against Denmark on Monday