Hoolahan shows his true worth to Iireland
Midfielder provides the added creative spark which O'Neill will need in France
He's not the messiah, he's a Norwich boy.
For all the pre-match talk about the young guns who hoped to move a few steps up the ladder and sneak onto that plane bound for France in the summer, it was one of the oldest of the old-stagers who made the biggest statement of all.
Wes Hoolahan has to start for Ireland at Euro 2016 if this team is to hold out any hopes of progressing from the group for the first time in a European Championship finals. The Republic of Ireland are a different side with, and without, the man called Wesley.
The gap between the dull fare of Friday night, against the Swiss, to the thrills of last night's 2-2 draw with Slovakia, where we were treated to three goals in the first 23 minutes, was only a few days but a big lesson in between.
Set-pieces are a big part of any side's arsenal. And this Ireland team use those dead-ball situations, usually from the boot of Robbie Brady, to effect.
Hoolahan was on the scene in the League of Ireland enough to know that the St Patrick's Athletic side which played out great battles with his beloved Shelbourne were - however unfairly - known by some as Set-Piece Athletic.
No shame in chances being created, goals being scored and points being won from the craft of a dead-ball play by someone like Martin Russell, a player who - like Hoolahan - was schooled by the people at Belvedere in Dublin in how to play the game.
Likewise, this Ireland side, if it can use dead balls to get something, then every goal and win will be hailed.
The goal which beat Switzerland last week, the goals carved out last night, both from the penalty spot, go down in the record books in the same ink used to describe the goals created from genius and brilliance.
But we can't rely on them to get us out of the group in France, as we saw when Brady, on as a half-time sub, tried his luck from a free-kick on 70 minutes, a poor effort from the Norwich man which never troubled Slovakia keeper Matus Kozacik.
We were fortunate to get two penalty kicks from the benign Norwegian referee Ola Ober Nielsen, the first a very unfair decision to punish the away keeper when he and Shane Long clattered into each other, the second more a case of clumsiness than malice from Martin Skrtel when he felled Long in the box.
And that's why Hoolahan is necessary to Martin O'Neill, to Ireland and to Ireland's hopes of avoiding another wooden spoon experience in Europe.
Hoolahan sparked some life in Ireland when he came on as a sub on Friday night and while the team didn't fall apart when he went off with 18 minutes to go last night, he had done enough to make his point: bringing Hoolahan to France but sitting him on the bench could make the summer very hard to watch through Irish eyes.
Glenn Whelan is the most-criticised Ireland player in some time, but those who nastily, and without justification, pick holes in Whelan's game should accept that Whelan's value is only evident when he's not in the side.
Same with Hoolahan. Last night he was the one player in a green shirt who craved the ball at all times, looked for openings, tried to make things happen. We saw Eunan O'Kane look enthusiastic, James McClean battled for 90 minutes in an unfamiliar role, but not much else was gleaned.
This midfield formation, which O'Neill has deployed a few times now, is hard for the players to get used to, but it's still a lot more effective, and a lot easier on the eye, than the solid 4-4-2 which we saw last week,and in the build-up to Euro 2012.
The paths to the finals are looking similar so far: a morale-boosting unbeaten run on the way there, a batch of clean sheets (though not last night) giving false hope, which was then dashed at the finals in Poland. The worst thing for Ireland would be for the manager, fans and the team to play up the unbeaten run and hope it's good enough to carry us through in France.
Slovakia's manager Jan Kozak said little of interest in his pre-match press conference, but he did stress the difference between the football played in qualification and the type needed at a major championships.
To get out of the group in France we need to create, and we need Hoolahan in the side to do that.
That apart, O'Neill will have learned little last night, and he has a new injury problem to contend with, keeper Rob Elliot now possibly out for the season.
And the damage which a tired-looking Slovakia side did to Ireland last night with their two goals could well be repeated in the summer.