The contest was over, but the moment was striking: 28 minutes into Mayo’s Saturday nightmare in McHale Park, Diarmuid Connolly made a mistake. He was correctly called for over-carrying with Dublin at full throttle.
Before that Connolly had been close to faultless as the counter-attacking visitors' rattled off 2-10 in 20 minutes. It would take a patient man to untangle some Allianz League form lines this March, but Dublin’s transformation from mediocre to masterful appears a simple case to shut.
Connolly was playing his first game of the spring. O’Sullivan had started none and come on in two. Stephen Cluxton was between the posts for the second time; Paul Flynn in the 15 for the first.
They were not the only boys in blue to play well; indeed it is hard to find a Dub who didn’t. It has been clear for some time that these four are some of the men who make Jim Gavin’s side tick.
O’Sullivan rivalled Connolly for impeccable use of the ball. He is the pendulum that moves Dublin from defence to attack.
Cluxton is arguably as gifted a footballer as either: there he was in the 14th minute, spraying a 50-metre pass off the outside of his left boot into Denis Bastick’s bread basket.
Flynn, back from groin surgery, was not quite as polished, which sounds ridiculous considering his contributions ranged from a killer pass for Bastick’s goal to an improbable dispossession on the edge of his own ‘D’.
Michael Darragh Macauley is arguably as important to Dublin as those four and still to return.
Who else? You could make a case for Rory O’Carroll, who ensured that Alan Freeman had another fruitless night.
Ciaran Kilkenny offered compelling evidence against Mayo that he could join the ranks of automatic selection. We forget sometimes he is only 22.
Beyond those, there is scarcely an irreplaceable Dub, but with the leading players back on stage, the support cast looked truly convincing for the first time this season.
Eoin Culligan is a rookie who was able to project confidence despite keeping Aidan O’Shea company for long spells.
Kevin McManamon, some people’s man-of-the-match (we would not look beyond O’Sullivan), always appears most damaging when the fulcrum of the side is intact.
There was a monotony to Dublin’s excellence pre-Donegal in 2014 and we could be set for more of the same.
Judgement will rest like it always does on one or two days in late August and September, but their collapse against Donegal does not invalidate Dublin’s placing as pre-Championship favourites.
Anything can happen in those madcap late-season minutes in Croke Park; we can only talk of who is most likely to prevail for there are no championship certainties when only the big boys are left.
Still, if Dublin remain tortured by what happened after Connolly missed his killer goal chance in that All-Ireland semi-final, they have little to worry about compared to most rivals.
Dublin have won five of the last six important competitions they have entered and it is hard to see what can keep them from claiming a 10thLeinster championship in 11 tries.
That is beyond even their mid-to-late-70s standards. Only Kerry have a comparable claim to compelling reasons for self-assurance.
Mayo still sit above Dublin, but scarcely has a league table lied more brazenly. Pat Holmes and Noel Connelly face every problem except over-confidence.
Before Saturday, there were plaudits for their deployment of Aidan O’Shea, how they varied use of the Breaffy man between the half- and full-forward lines.
Now, what looked canny when Monaghan were being sent to the sword is taken as evidence of uncertainty when Dublin are doing the filleting.
It is a similar story with Kevin Keane’s rehabilitation at full-back and Donal Vaughan’s new role; no innovation looks clever in the shadow of a 14-point deficit.
Things will improve when Cillian O’Connor returns, for he is as important to Mayo as any of Dublin’s big five and probably more so.
Of more concern than players and their positioning was the general hesitancy and sloppiness with which Mayo approached a big game against a big rival in front of a big home crowd.
James Horan, in his TV punditry role, spoke of his surprise at the lack of “concentration, focus and level of aggression… all those things that are synonymous with Mayo”.
It was fair summary. Only Keith Higgins seemed close to the correct wavelength.
Perhaps that is a problem that can be fixed, but the wider one is that this is the continuation of a two-year trend. Mayo have not been fluid and fearsome since 2013, not in the way Dublin are.
We remain mindful of last season’s surprises. Nonetheless, it is too tempting to point out that perhaps the most relevant aspect of the Championship draw is that Dublin and Kerry are on opposite sides of it.