Republic of Ireland v Bosnia-Herzegovina: Martin O'Neill on the brink of promised land
This is a night where the result is the only thing that matters.
For Martin O'Neill, it will provide either a beautiful or brutal example of the contrast between the club and international sphere.
When the Derryman accepted the job as the Republic manager, he predicted that it would take him a while to get his head around the gap between matches and that initially proved to be the case.
Last November's defeat to Scotland lingered through the winter, killing the good vibes that had been created from late goals in Georgia and Germany.
If the Republic fail to get the job done against Bosnia in the second leg of an evenly matched Euro 2016 play-off, there is still a feeling that O'Neill has settled in the job to the extent where he will sign a new deal which will keep him in charge for the next World Cup tilt. But the build-up to that mission would essentially consist of what ifs and if onlys. Ten months of regret.
That's because a campaign which at one point seemed to be slipping away from Ireland has now reached a climax which O'Neill would have accepted at the qualifying draw in Nice last year. He would have taken it at any point last week, too, given Zenica's reputation as a venue that shatters the dreams of visiting sides.
The Republic emerged with their French ambitions intact and, while the comical levels of fog has prevented the management team from engaging in the usual level of analysis, they know they achieved a fine result without playing well.
Robbie Brady articulated that point in the aftermath of the chaotic final ten minutes which started with his precious away goal.
Bosnia expect to lift their performance levels, too, but after a build-up which almost exclusively focused on the strengths, round one highlighted the flaws which left them needing this tiebreaker in the first place.
With the memories of the famous win at Germany fuelling the belief that home advantage actually stands for something again, and the return of Jon Walters and possibly John O'Shea and Shane Long leaving the hosts with a stronger hand, O'Neill is on the brink of something special.
"It's not about my managerial career," he stressed. "It's about the Republic of Ireland trying to win a game to get to France. I don't think I could put it in more simple terms."
The perception from outside is that the odds have shifted in favour of the unseeded side in this pairing.
From the Republic's perspective there is a lingering fear, however, that the quick concession to Edin Dzeko after Brady's goal allowed the Balkans off the ropes. After being so efficient in terms of notching late goals in the campaign, it was a surprising lapse of concentration.
It recalled the euphoria of Robbie Keane's breakthrough goal against Turkey in the first leg of the Euro 2000 play-offs, a jubilation which also lasted for just four minutes as a sloppy penalty concession proved costly. Valuable momentum was lost.
The difference, of course, is that the Turks banked the away goal on that occasion and ended up getting the scoreless draw in the return that facilitated progression. The Republic kick off this decider with the crowd on their side and the knowledge that a clean sheet will do.
O'Neill has dismissed the notion his team will set out with the intent of shutting up shop, stressing that it would be a dangerous plan as Bosnia have the attacking quality to conjure a goal from nothing.
"We have to try and win the game," he asserted. "If we set out with any other sort of mindset, things might not work out for you."
There is no reason to doubt the sentiment but, if the game happens to be scoreless at the midway point, the Irish ambition to go for the jugular will be tested.
Sometimes it can be a subconscious reaction rather than a specific instruction, but experience tells us that the temptation to attempt to close the game out will kick in at some point.
This is where intrigue is added to the team selection, especially as the presence of Long and O'Shea at the final training session has opened up the possibility that they could have a part to play.
The 63-year-old has acknowledged that the possibility of extra-time and penalties will have to be factored into his thinking and, given the prominence of the 1-1 draw in Irish football history, that is a wise course of action.
He has used his bench cleverly during the campaign and if Long is anywhere close to fully fit then he would be an ideal option to keep in reserve for a situation where Ireland are under the pressure and in need of an out ball.
The Germany game is the perfect illustration of that point.
The suspicion is that James McClean, Robbie Keane and Aiden McGeady are in the emergency sub bracket too, although the former should expect to be involved at some stage regardless of the state of play.
When he ponders taking a risk on O'Shea, the Irish boss will have to be absolutely sure he is 100% able to last the duration as otherwise he is in danger of wasting an attacking change that could be required to save the day.
The change to the rearguard which is anticipated is Marc Wilson coming in ahead of Stephen Ward at left back, although it was a topic that O'Neill was reluctant to discuss.
"Stephen did fine (on Friday) but he hasn't played much for Burnley," he said, "He's a natural left back for us, who has never let us down."
If Ireland burst out of the blocks and take the crowd with them, they can embrace a golden opportunity.