Denmark and Ireland ground out a 0-0 draw on Saturday, meaning they'll both be fancying their chances of bagging a ticket to Russia in the second leg.
Denmark coach Age Hareide had in fact said he was keen on a 0-0 in the first leg, as they'd then have "120 minutes to get a goal in Dublin". O'Neill will be a little worried that his Irish side caused Denmark so few problems in Copenhagen, but he'll be entirely happy if at the end of the day one long ball over the top falls kindly for Murphy to stab home and send Ireland to the finals next summer.
Either way, don't expect this to be the greatest game of football you've ever seen technically, but for nerves and tension as the clock ticks down it could be a cracker.
What time does Ireland v Denmark start?
The crunch qualifier between the Irish and the Danes starts 20:45, so expect penalties about 23:00. Find out what time the match starts around the globe.
What TV channel is showing Ireland v Denmark?
Can I watch Ireland v Denmark on internet streaming?
Almost certainly. The game is available in most nations through the rights holders' online platform such as fuboTV in the United States and on Sky's streaming service. Your best bet is to check who is showing the game in your country, and if they have an online service or iOS/Android app to watch it on.
Ireland v Denmark live on AS English
Minute-by-minute meister Robbie will be covering the game in its entirety, so head over to his live coverage for in-depth analysis and maybe even the occasional joke.