Monday's encounter in Cardiff has the potential to be one of the most important games in either country's recent history; Wales are targeting only their second appearance at the World Cup finals, and Republic of Ireland pursuing a spot at international football's elite competition for the first time since 2002.
Both nations could still win Group D but with Serbia expected to beat Georgia this is more likely to be a straight battle for second spot and a place in November's play-offs.
A win for either side guarantees at least a play-off place, while Wales could still qualify with a draw depending on the result between Ukraine and Croatia in Group I.
The visitors will need to win but if recent history in this fixture is anything to go by, Ireland should take a reasonable amount of confidence into just the fourth competitive meeting between the nations.
Despite Ireland's recent superiority in this fixture, which has seen Wales fail to score in six of the last seven meetings, replicating their recent form when heading across the Irish Sea to the Welsh capital may not be enough to secure a passage to next month's play-offs. In fact, a draw could see both sides miss out given that only eight of the nine runners-up qualify for November's two-legged ties. The last three meetings in Cardiff have finished level, in what has been historically a particularly tight fixture.
Wales' last win came over 25 years ago, a 1-0 friendly win in Dublin, and they have failed to win any of the last four meetings on home soil, last tasting victory in Swansea in September 1979. Prior to March 2017, the only previous competitive meetings were in qualification for Euro 2008 - neither qualified as Czech Republic and Germany dominated Group D, with Republic of Ireland finishing third, and Wales fifth.
History favours the visitors on Monday, although they will need to inflict a first competitive home defeat on Wales in over four years. Ireland will be hoping luck is on their side, and history is in the mood to repeat itself if they are to board a plane to Russia next June.