Off-key Leinster unable to recover after disastrous opening half
Leinster 15 Scarlets 27
The script was written before a ball was even kicked but no one told the Scarlets as their 14 men ripped up the history books and stunned Leinster to advance to next week's Guinness PRO12 final.
The majority expected an all-Ireland decider at the Aviva but the Scarlets were rewarded for their consistently fearless approach across the season as they tore the Leinster defence to shreds.
Prior to last night, no away team had ever won a PRO12 semi-final and despite Steff Evans' red card just before the break for a dangerous tip tackle on Garry Ringrose, the Welsh side managed to hold on for a stunning victory
Three first-half tries from the visitors silences the home crowd. This was a disjointed Leinster performance, littered with uncharacteristic errors, as they missed the chance to avenge last season's final defeat.
Johnny Sexton had a rare off night and with his lack of control, Leinster struggled. The Ireland out-half shipped a knock midway through the first half and never looked right after it.
That said, when you haven't played a game in almost four weeks, it was always going to be a tough to get up to speed in a semi-final against a quality Welsh side.
Leinster grew into the game in the second half thanks to their numerical advantage but by that stage, the damage was already done as the Scarlets had built a 21-10 half-time lead.
To add to Leo Cullen side's woeful first-half display, they lost Jack McGrath (arm) and Luke McGrath (HIA) to injury. Rhys Ruddock would later follow the scrum-half off with a head injury.
Jack McGrath now faces an anxious wait to determine the extent of his injury less than two weeks before the Lions depart for New Zealand.
All told, it was a night to forget for Leinster who had started the game very brightly.
A Sexton knock-on, however, gave Scarlets an attacking scrum which eventually led to Evans silencing the home crowd after eight minutes.
Adam Byrne shot up off the line and missed the tackle. That allowed Davies to free his hands and release John Barclay who in turn fed Evans. After that it was all about the speedy winger's pace as he sprinted clear and under the posts to allow Rhys Patchell slot the easy extras.
Matters got worse for the hosts as Jack McGrath was forced off and replaced by Cian Healy.
Sexton dropped to the deck after a hefty hit and required attention, all the while Lewis Rawlins was pinged for not releasing. With Sexton still being attended to, Isa Nacewa assumed the kicking responsibilities and put Leinster on the board.
Leinster didn't have to wait long to get over the whitewash as Garry Ringrose finished off a stunning move off a brilliantly-worked set-piece move.
Sexton and Jack and Jack Conan linked well before Ringrose took over and turned on the afterburners to score. Nacewa's conversion put Leinster 10-7 in front after 24 minutes.
That was as good as it got for the hosts in an error-strewn first half however. Jamison Gibson-Park had his box-kick charged down by former Leinster lock Tadhg Beirne who came back to haunt his old club.
Gareth Davies was left with a two-on-one and he duly fed Aaron Shingler who dotted down under the posts. Patchell's dropped conversion put the Scarlets back in front just two minutes after Leinster had taken the lead for the first time.
Sexton was furious but his restart dropped short, which allowed Scarlets another foothold. They eventually took full advantage with Davies the latest to score for the Welsh side.
Patchell's conversion pushed the Scarlets into a 21-10 lead and when Sexton got involved with Davies off the ball, it summed up Leinster's frustrations.
It all played into the Scarlets' hands but their famous win came under serious threat two minutes before half-time when Evans was deservedly shown a red card for his tip tackle on Ringrose, who was lucky to avoid a serious injury.
The crowd were incensed and after referee Mitrea carefully consulted with his TMO, Evans walked.
The errors continued after the restart. Tadhg Furlong went off with cramp on the hour mark at the same time Sexton misjudged another kick and put the ball out on the full.
But with 15 minutes left on the clock, it was Scarlets' turn to commit hara-kiri as an overthrow deep inside their own 22 was collected by James Tracy. Dan Leavy carried just short of the line but Conan was never going to be stopped as he bulldozed his way over.
Nacewa however missed the conversion from in front of the posts which typified the uncharacteristically sloppy nature of Leinster's performance.
Just as Conan's try looked like it would give reignite Leinster's challenge, Healy was pinged at scrum time and Liam Williams stepped up and slotted the pressure kick to push his side back into a nine-point lead (24-10).
On his return to the RDS, Beirne was outstanding and it was his turnover that forced a crucial penalty deep inside the Scarlets 22 with eight minutes left. That was the cue for the Leinster supporters to head for the exits.
They had seen enough but Scarlets weren't finished there as Williams added another penalty for good measure after Healy was penalised for a high tackle.
Leinster picked a bad time to lose their first league game at the RDS since February 2015 and it was one that they will live to regret for a while yet.
Leinster - J Carbery; A Byrne, G Ringrose (Z Kirchner 73), R Henshaw, I Nacewa (capt); J Sexton (R Byrne 79), L McGrath (J Gibson-Park 23); J McGrath (C Healy 10), J Tracy (R Strauss 70), T Furlong (M Bent 60); R Molony, H Triggs (D Toner 51); R Ruddock (D Leavy 46), J van der Flier, J Conan.
Scarlets - J McNicholl; L Williams, J Davies, S Williams, S Evans; R Patchell (H Parkes 60), G Davies (J Evans 51); R Evans (W Jones 56), R Elias (EPhillips 71), S Lee (W Kruger 65); L Rawlins (D Bulbring 65), T Beirne; A Shingler, J Davies (DTH van der Merwe 79), J Barclay (capt) (W Boyde 63).
REF - M Mitrea (FIR)