Ospreys are all-but assured of their place in the Pro12 play-offs after Saturday's 24-10 victory over fellow contenders Ulster.
The two sides came into the meeting separated by just one point, Ospreys occupying the fourth and final qualification place ahead of their visitors.
But after this victory, Ospreys are five clear and with a vastly superior points difference heading into the final weekend, only a heavy defeat at Scarlets combined with Ulster thrashing leaders Leinster would deny the Welsh side.
Much of Ospreys' hard work was done in the first half at the Liberty Stadium as tries from Tom Habberfield and Tyler Ardron gave them a 17-3 lead.
It remained that way until the final two minutes, Brendon Leonard going over for Ospreys - whose celebrations were hardly dampened by Jacob Stockdale's subsequent consolation.
Scarlets made sure of their place in the play-offs with a convincing 30-8 win at Connacht. The visitors scored five times - two of those by Steff Evans, meaning they and Ospreys will meet to decide third and fourth next week.
One of them will face Munster, who secured a home semi-final as they ran in five tries for a bonus-point 34-14 success at second-from-bottom Treviso, including a brace for Darren Sweetnam.