Who writes their scripts, eh? Connacht cast aside desperate form to dismiss the abysmal efforts of European champions Leinster and the only surprise was that it took until the 84th minute for George Naoupu to wrap up the bonus point.
Ronan Loughney's late fifth confirmed a defeat that smashed a glut of records. Dan Parks, a new local hero, can retire happy now.
"We won't get carried away," said Connacht coach Eric Elwood, as Connacht fans celebrated as if acclaiming the end of prohibition.
"It's a great night, no doubt. But we're calm inside. The lads deserve it, the way they played and the scores they got. People will say we did a Leinster on Leinster. Now we need to do this on a regular basis.
"We've been hurting over the last few weeks because our defence has been poor, so to keep a team like Leinster scoreless is outstanding. And I thought we scored some nice ones ourselves.
"That's one of the best performances I've overseen in my time here. We're enjoying the moment, but we're not going to get carried away.
"The challenge is to replicate a performance like that in Ulster next weekend. That's going to be an even harder challenge."
It was a truly humbling night for the wretched champions of Europe, for whom hell may have been a more preferred venue than Connacht on this night of nights.
Connacht's utter superiority rendered them mere chumps.
Joe Schmidt's embarrassed, humiliated men might have been advised to take a walk around some fields of Athenry, merely to taste the loneliness and despair of such a thunderous defeat.
Leinster not only headed east with their heads bowed and spirits cowed but a lengthening injury list -- as Gordon D'Arcy (ribs), Rob Kearney (back), Quinn Roux (shoulder) and Shane Jennings (leg) were all forced off early.
"We were out-passioned," moaned Schmidt. "It's humbling. Preparation equals performance. Ours wasn't perfect. And losing players didn't help. Connacht deserved their win.
"Our lack of fluidity is evident in our performances so far. We need to get continuity but we don't have much time. It's going to be very, very tough. Some individuals will be very disappointed with their performance tonight."
The early signs had been ominous for the champions as Connacht tore into them unrelentingly, typified by Johnny O'Connor's welcome home present to Fionn Carr, a crunching tackle that sent the bewildered winger into touch.
Leinster scored the opening points but they would barely land another punch all night as their pack was subsumed by the warrior eight in ruck and scrum, and their midfield and fringe defence constantly punctured.
Their limited attacks looked pretty, but were ultimately pretty ineffective, despite some shapes from Ian Madigan; had he and his callow colleagues in the back-line been more devout in defensive duty, Leinster's humiliation might have been limited a tad.
Connacht were in unforgiving mood though.
They were far more menacing and penetrative in attack, much more assured on their own ruck ball; with the half-backs dominating control and their pacey, powerful three-quarters looking much more forceful in running.
Connacht deserved their opening try, benefiting from the gaping hole in Leinster's midfield as the wonderful scrum-half Kieran Marmion sent Dave McSharry scuttling clear for a facile seven-pointer.
A beautiful curling Madigan penalty, redolent of a sweet draw in Medinah, brought Leinster back to 6-7 but they were merely staunching the bleeding.
Connacht's second try was culled directly from the European champions' playbook; A sweeping right-left move -- ball in front, passing crisp all the way -- culminating in Leinster's drift being horribly exposed as somehow John Cooney was left to face the marauding Fetu'u Vainikolo.
There would only be one winner.
Connacht now led 14-6 as Parks converted once more and the 5,813 mostly Connacht support were rocking to an unfamiliar beat of vast superiority against their much-vaunted rivals.
With Brendan Macken binned and Kearney joining the sick bay, the home side sensed blood.
Connacht's third try was another sweeping effort and indeed it was effectively constructed, which makes Leinster's pathetic attempt to defend it even more inexcusable.
The hapless Carr will be the target of most of the Leinster wrath for his wafer-thin tackle attempt on try scorer Tiernan O'Halloran, but the rest of his colleagues were equally at fault for their soft defence as the ball made its way to the right wing.
Parks missed the conversion; well, everything he touched couldn't quite turn to gold now, could it? As delirium delivered itself to the stands, he did have the final word with a booming penalty to give his side a 22-6 lead.
Connacht were cruising. Shamefully, Leinster were more effective without the ball, than with it, their rate of turnovers ploughing, desultorily, well into double figures.
The pill was a liability for them. Connacht needed no drug to sustain them on this night of nights.
Simple adrenalin, and no little skill, sufficed on a famous day way out west.
They celebrated as if European champions themselves when realistically they should aspire to a level such as this with much more consistency, not just when the big guns come to town.
Connacht -- R Henshaw; T O'Halloran, E Griffin, D McSharry (M Fifita 78), F Vainikolo; D Parks (M Nikora 78), K Marmion (D Moore 78); D Buckley (B Wilkinson 53), A Flavin (J Harris-Wright 57), N White capt (R Loughney 49), M Swift, M McCarthy, E McKeon (D Gannon 50), J O'Connor (W Faloon 53), G Naoupu.
Leinster -- R Kearney (I Nacewa 32); F McFadden, B Macken, G D'Arcy (N Reid 11), F Carr; I Madigan, J Cooney; Heinke van der Merwe (C Healy 46), T Sexton (S Cronin 46), J Hagan (M Ross 46), Q Roux (D Toner 13), T Denton, B Marshall, S Jennings capt (J Murphy 60), L Auva'a.
Ref -- P Fitzgibbon (IRFU)