Scarlets head coach Nigel Davies hailed his team's 31-17 triumph over Stade Francais as a "new start" for the Welsh region.
The Scarlets had failed to win in their previous 11 games in the Heineken Cup before upsetting the odds with victory over the French giants.
But tries from David Lyons and two from young centre Jonathan Davies, along with 16 points from the boot of Stephen Jones, clinched an unlikely win.
Davies said: "This was all about us re-establishing our European credentials with a big win and an even better performance. It's good to finally end that run of losses. Hopefully this is a new beginning for us and there are more similar results to come.
"We felt this performance was never far away. We spoke as group that we had produced good rugby in patches but never for the full 80 minutes. This time we did."
The result also confirmed Harlequins as Pool Four champions, despite yesterday's 21-10 defeat to Ulster. Davies said: "We've done Quins a big favour but we're not bothered about that.