La Rochelle saw off Toulouse - with Alexis Bales central - while Castres beat Agen in the Top 14 on Sunday.
The Champions Cup final may be the main course for rugby fans this weekend, but French sides Clermont and La Rochelle will first b…
Clermont had not been beaten since October, but they were brought back down to earth by Top 14 champions Castres.
Scarlets' first Champions Cup knockout clash since 2007 saw them beat La Rochelle to reach the semi-finals.
Montpellier were replaced by La Rochelle at the summit of the Top 14 table after losing at Stade Marcel-Deflandre.
Toulouse have now won their last four Top 14 games after beating the champions, while Racing 92 suffered a third consecutive loss.