It's the Welsh side that advance to the Pro 12 final
Leinster have missed out on a place in the Guinness Pro 12 final after a 27-15 defeat at home to Scarlets in their playoff semi final.
The Welsh side led throughout despite being reduced to 14 men just before half time as a lacklustre Leinster failed to sparkle at the RDS.
Scarlets took a 7-0 lead when Steff Evans raced clear to score the first try which was converted by Rhys Patchell.
An Isa Nacewa penalty then reduced that gap, before Garry Ringrose got in for a 24th minute converted try as Leinster took a 10-7 lead.
But two tries from Aaron Shingler and Gareth Davies had Leinster reeling as the Scarlets stretched their lead to 21-10.
Scarlets' Steff Evans is sent off by referee Marius Mitrea after a tackle on Garry Ringrose of Leinster ©INPHO/Tommy Dickson
But the Welsh side suffered a setback shortly before half time when Steff Evans was red carded for a dangerous tackle on Ringrose on 38 minutes.
A Jack Conan try on 64 minutes put Leinster back within touching distance but crucially the conversion was missed by Nacewa.
Despite the man advantage, Leinster struggled to find another try as two late Liam Williams penalties saw Scarlets stretch their lead to 12 points by the final whistle.
Munster and Ospreys go head to head in the other semi final on Saturday in another Irish-Welsh clash for a place in the final.