Luke Fitzgerald crossed twice and Brain O'Driscoll grabbed another as the Heineken Cup finalists showed off their attacking talents in their last home game of the season.
Fitzgerald scored twice in the first-half to give his side a 21-8 interval lead and then four more tries flowed after the break. O'Driscoll waltzed away for one of them and 2005 Lion Shane Horgan helped himself to another.
Defeat leaves the Scarlets, who started with their two Lions, Stephen Jones and Matthew Rees, locked in a desperate battle with the Dragons and Blues to avoid having to travel to Italy to face a play-off for a place in next season's Heineken Cup.
If either the Blues, who host the Scarlets on Wednesday, or the Scarlets have to play the Italians then they will do so without their Lions as the play-off game comes the day before the Lions kick-off their 10 match tour against a Royal XV in Phokeng, near Rustenburg.