If Group D table-toppers Serbia, who host Georgia this evening, lose for the second consecutive game, whoever wins the crunch clash between Wales and Ireland will secure an automatic spot in next year's footballing showpiece in Russian Federation. If both the Wales and Croatia games are draws and the Croatia game has one more goal (say 1-1 against 0-0) then Croatia will qualify for the play-offs ahead of Wales on fair play.
The winners in Cardiff will guarantee at least second in Group D, with a draw enough for Wales to end up in that position and, potentially, claim a play-off spot for Russian Federation 2018.
Serbia's Aleksandar Prijovic celebrates with his teammates after scoring a goal, during the World Cup Group D qualifying soccer match between Serbia and Georgia at the Rajko Mitic stadium in Belgrade, Serbia, Monday, Oct. 9, 2017.
That dream looked over last month after the defeat to Serbia left Ireland needing to win their two November games and hope that results in other groups fell their way.
"We played really well in patches and created plenty of chances throughout the game, so we can use that and go forward into the Israel game tomorrow full of confidence".
How can I watch Wales vs Ireland? We're still going to be depending on results from Tuesday evening but the certainties are now Italy from Group G and Croatia from I.
Winger McClean beat Wales in this must-win game with a brilliantly worked team goal that keeps Ireland's hopes of being in Russian Federation next summer alive.
"We changed the side to give us energy for a big game in Lille against Italy at the European Championships".
'The players have proven this is a golden era, ' Coleman said. "The confidence will do us the world of good going into Monday".
Chris Coleman (Wales): "We're on unsafe ground if we go in with a game plan of trying to soak the pressure up for 90 minutes".
Wales are slight favourites for the win with the draw priced at 2/1.
This game saw 58 aerial duels contested - the most in a single game during in this UEFA Qualification campaign for World Cup 2018.