Scarlets produced an outstanding display at RDS Arena on Friday, overcoming the first-half dismissal of Steff Evans to reach the Pro12 final for the first time with a stunning 27-15 victory over Leinster.
Wing Evans scored the first of three tries for the Welsh region, but was sent off shortly before half-time for a tip tackle that saw Ireland international Garry Ringrose land dangerously on his head.
However, despite being down to 14 men, Scarlets were able to absorb significant pressure in the second period and make history by becoming the first away team to win a Pro12 semi-final.
Wayne Pivac's side will now face Munster or the Ospreys in next weekend's final. No Welsh side has won the competition since the Ospreys triumphed in 2012.
Leinster had dazzled with their attacking prowess in the regular season, yet it was Scarlets' front-foot play that stood out in the first half and ultimately proved decisive.
Evans rounded off a slick move down the left to open the scoring, before an Isa Nacewa penalty and a fine try from Ringrose briefly edged the hosts in front.
Gareth Davies then took centre stage, putting Aaron Shingler over - amid suspicions of a forward pass - and scoring himself after an offload from the excellent James Davies had opened up another gap in the Leinster defence.
The subsequent dismissal of Evans, with Scarlets 11 points to the good, understandably limited the visitors' attacking intent.
However, Leinster could only find one try in the time that remained - through Jack Conan - and two late penalties from Liam Williams made the game safe for Scarlets.