It ended, over two hours later, with Kildare taking the spoils after a pulsating encounter that stretched into extra-time where it was finally settled by an emphatic 1-2 scoring burst by super-sub Tomás O'Connor.
At different stages - such as when they led by two points with five minutes remaining in normal time, or when holding a three-point cushion at the midpoint of extra-time - Dublin looked firmly in the box seat.
Yet they were never home, certainly not hosed, and Kildare never stopped snapping at their heels. By the finish, the visitors had far more experienced campaigners on the field and this probably proved decisive.
Yet it was also an evening when, for all the understandable talk of the youthful riches at Jim Gavin's disposal, the Kildare young guns stood tall. On this beguiling evidence, Niall Kelly, Paddy Brophy and Daniel Flynn are names well worth tracking over the spring months.
"Probably the most pleasing part was we had four under-21s on for most of the game and I thought they all acquitted themselves very well," declared Kieran McGeeney after watching his team squeeze home by 1-16 to 0-17.
By the same token, his opposite number was "absolutely" disappointed with the outcome but mindful of the bigger picture. "Any time a guy pulls on a Dublin jersey or you manage a Dublin team, you want to win. But in the context of the game, it's a pre-season tournament," Gavin reminded.
"There is a long road ahead. I've always said to the guys I'll be honest with them and give them as much opportunity as possible to stake a claim, so for that purpose it was an excellent opportunity for them and for me."
He intended to start making cuts to his extended Dublin squad "over the next 24 hours" with plenty of hard calls to be finalised. "It's very fluid at the moment because there are so many away, but we are striving for 30 guys at the back end of the National League."
On that score, Saturday night will have been far more instructive for Gavin than the previous week's cakewalk.
High-quality matches of this ebb-and-flow nature aren't meant to happen in January, even less so on a squelchy surface like this. Yet every once in a while, for no pre-ordained or obvious reason, they do.
Last year, the same two counties met in the same competition and it was a drab affair, won comfortably by the Lilywhite hosts.
But this encounter started at 90mph and even though scores were initially thin on the ground, it soon took on a life of its own. With every passing minute the intensity ratcheted up and points started to fly over from myriad angles and you were left in no doubt that, albeit this was "only the O'Byrne Cup", the outcome mattered. Intensely.
So much so that, in the death throes of extra-time, some lax refereeing fuelled the eruption of a brief melee that culminated in a straight red card for Denis Bastick. The Dublin midfielder now stands to miss their Allianz League opener against Cork next Saturday night, but that one disciplinary blemish shouldn't detract from the many positives on show here.
Kildare can derive more, and not just because of the result. Of the rookie brigade, Niall Kelly and Paddy Brophy may be straight out of minor but you'd never have guessed. Kelly was assured and accurate in possession while kicking a rapid-fire brace, late in the first half, one off either foot. The powerful Brophy also excelled in that opening period and finished with 0-3 from play.
Yet our marginal choice for Man of the Match was another newcomer, Daniel Flynn, who excelled in the possession stakes after switching to midfield late in the first half.
The other key to victory was the impact of Kildare's more experienced brigade coming off the bench. With his first touch, Pádraig O'Neill landed the 68th minute equaliser that would force extra-time.
And while fellow subs Mikey Conway (from a '45') and Seánie Johnston (from in front of the posts) squandered injury-time chances to crown Kildare's comeback, they would eventually get there despite falling three points adrift once more.
Enter Tomás O'Connor, who had already caused a few frissons of panic before his all-important goal, 45 seconds into the second period of extra-time. Declan O'Mahony appeared to have won possession but in the ensuing goalmouth scramble, O'Connor emerged with the ball to fire home.
Now, suddenly, Kildare had momentum and their goalscorer duly turned the screw on Tomás Brady, claiming balls inside from O'Neill and turning away from his marker to score a point off either foot.
For Brady, it was arguably his steepest challenge since switching from the Dublin hurlers - but full-back is an unforgiving position when your opponent is feeding off such inviting passes.
Conversely, having started the game in lively 'assist' fashion, Bernard Brogan's influence waned (just as Ollie Lyons' soared) partly because Dublin's delivery inside became increasingly ragged.
Still, even in defeat, Gavin can take his share of positives too. Of the younger brigade, Jack McCaffrey showed he can supplement his counter-attacking flair with some timely defensive blocks too, while Paul Mannion (0-4, 2f) and substitute Cormac Costello had cameos of excellence before they, and their colleagues, eventually succumbed in the home straight of a minor classic.