Wales centre Jamie Roberts grabbed two tries to help Cardiff Blues smash the Scarlets 39-16 and secure a spot in next season's Heineken Cup.
The Blues were presented with two chances to claim a place in Europe's premier competition next term after also making it through to the semi-finals of the Amlin Challenge Cup.
The Scarlets as ever were able to depend on the boot of Wales fly-half Stephen Jones, who recently signed a new contract with the region, as he notched two penalties and a drop goal while Regan King also crossed in the first half.
But Cardiff were always dangerous and ensured they only trailed 16-15 at the break thanks to Roberts' first try and a Deiniol Jones score.
And the Blues showed their killer instinct with two tries sharply after the break from Taufa'au Filise and Roberts, before Richie Rees stormed over and Ben Blair slotted a penalty to wrap up the win.
After losing their Under-20s Six Nations crown to England Under-20s in a thrilling final round, France Under-20s lock Tristan Labouteley insists his side will be out for revenge at this year's Junior World Championship.