This was the kind of night Connacht dream of as they plot their vision of the future.
This morning, the western province peer down at the rest of the Guinness Pro12 having won their opening three games of the season for the first time.
They did it by beating the team they love to beat the most in these parts, ending a long wait for a win over one of their provincial rivals in front of a sell-out crowd of 5,971.
Leinster must have been mystified as they retreated down the M6. They utterly dominated the first half, but were met with a green wall of defiance led by the outstanding John Muldoon.
The difference was provided by a moment of brilliance by Kieran Marmion, whose 56th-minute try in front of the watching Joe Schmidt lit up the Galway night.
"He's a class player, you know. More important he's gutsy, I've never met anyone as gutsy," coach Pat Lam said. "If I was still coaching Super Rugby, he's be a starter in my team easily, he's that good."
It had all looked so ominous for the hosts barely an hour earlier as Leinster hit the ground running and led 9-0 after 15 minutes.
They wouldn't score again as, somehow, Connacht made it to half-time within a converted try of the visitors despite being behind on territory, possession and penalty count.
Leinster had called TMO Seamus Flannery into action twice, but each time he ruled against them correctly.
Their early dominance was established at scrum time and reinforced at the ruck.
Ian Madigan opened the scoring after Mike Ross forced Denis Buckley to concede a penalty in the scrum, before Jack Carty missed a chance to level from in front of the posts.
Madigan missed with his second effort, but soon extended his side's lead to 9-0 as the penalties against green racked up.
It took a quarter of the game to elapse before Connacht gained any sort of foothold as Carty pulled a penalty back.
Muldoon was leading from the front with a couple of thumping tackles, but he got a little carried away and referee John Lacey brandished his yellow card when the skipper came in from the side at a ruck.
Leinster went for the jugular and thought they had scored when Madigan raced clear, but a second look showed Eoin Reddan's pass had been forward and the try was ruled out.
Despite openside Willie Faloon going off with a shoulder injury, Connacht coped well with 14 men and Robbie Henshaw got the home crowd roaring with a monstrous tackle on Jimmy Gopperth.
The Westerners had their dander up, but Jamie Heaslip diffused the threat by ripping the ball from Marmion's grasp and Brendan Macken took advantage by racing through the unprepared home defence.
Niyi Adeolokun caught him in the '22', but Leinster's forwards took over and a try looked inevitable as Lacey went upstairs again.
But the brave Connacht defence had held firm as Marmion managed to hold up Dominic Ryan and Mike McCarthy over the line. Muldoon returned and the scrum held firm as they escaped to the sancutary of the dressing-room.
Connacht clearly used the break to address their scrum issues as they forced a penalty out of Ross immediately after the break, but Leader's effort was off-target.
The hosts attempted to build on that by getting Henshaw into the game, but a combination of their own indiscipline and some 50/50 calls going in Leinster's favour meant the hosts found themselves back on their own line once again.
This time, their maul defence held up well, while Buckley forced a penalty to allow Leader to clear.
With the superb Muldoon continuing to take the game to the champions, Lam's side eventually got the break that almost lifted the roof off the Clan Terrace.
Having lived off scraps for most of the game, Marmion finally took the game by the scruff of the neck, spotting a missing pillar at the Leinster ruck, stepping Rob Kearney and touching down. Carty converted and suddenly the home side held the most unlikely one-point lead.
Now the penalties were flowing the way of the home side, but, again, they were shooting themselves in the foot, though, losing six of their lineout balls and kicking the ball dead.
Matt O'Connor sent for reinforcements with Cian Healy, Shane Jennings and Gordon D'Arcy introduced, but Leinster couldn't find a way through as George Naoupu and Muldoon continued to make big plays without the ball.
Gopperth spotted an overlap on the right for Eoin Reddan to chip over Leader, but Kearney's hack ahead went into touch and, while another Connacht's lineout went awry after Fergus McFadden was done for crossing, another brilliant scrum kept Leinster on the back foot.
Luke McGrath handed his side a lifeline with a break that gave Gopperth field position, but he couldn't pull the trigger on a drop-goal and the replacement scrum-half knocked on.
With Ronan Loughney in for his first and final play, the home scrum held firm and the Sportsground erupted to the sound of 'We are top of the league' as Matt Healy booted the ball dead.
All this and their Kiwis to come. Connacht are on the rise.
"We're a good team, a good team that works hard," Lam said. "We'll fight for everything, simple as that. We're not flashy, we don't have stars but we're building away and we'll keep our feet on the ground.
"We know it's not perfect, we said that in the changing room. We said: 'was it perfect?' and they said 'no'. Have we got things to work on? Yes."
CONNACHT - D Leader (C Ronaldson 69); N Adeolokun (F Carr h-t), R Henshaw, D McSharry, M Healy; J Carty, K Marmion (I Porter 69); D Buckley (R Loughney 80), D Heffernan, N White (R Ah You 65); A Muldowney, Q Roux (M Kearney 50); J Muldoon, W Faloon (G Naoupu 32), E McKeon.
LEINSTER - R Kearney; F McFadden, B Macken (G D'Arcy 59), I Madigan, D Fanning; J Gopperth, E Reddan (L McGrath 76); J McGrath (C Healy 46), S Cronin, M Ross (T Furlong 65); D Toner, M McCarthy; R Ruddock, D Ryan (S Jennings 65) (T Denton 72), J Heaslip.
REF - J Lacey (IRFU)