Leinster head coach Joe Schmidt admitted he was far from delighted despite his side winning 33-14 with a bonus point against the Scarlets.
The Heineken Cup holders scored their fourth try by the 44th minute at the RDS, with Rob Kearney adding to first half-efforts from prop Cian Healy, flank Shane Jennings and wing Luke Fitzgerald.
Five points boosted the Irish province's chances of sneaking into the knockout stages, but qualification could yet come down to the number of tries scored, with Schmidt left disappointed by their lack of clinical edge on Saturday.
"There already are (regrets). There are at least two more we should have got, one more where I felt there was good space and the ball was knocked down," Schmidt said.
"There is frustration but the reality is we are where we are and this is what we can plan to do and try to execute it."
Clermont cannot be caught at the top of Pool 5 but Leinster retain hope of qualifying as one of the two best runners-up, although a big win is needed against Exeter next weekend as well as some favourable results elsewhere.
"Leicester and Toulouse are both ahead of us but they have got to play each other. They can nullify that a little bit. I have a lot of respect for (Montpellier coach) Fabien Galthie," added Schmidt.
"He is a guy I have had a lot of chats with over the years, but I would like to see him beaten. It's dog-eat-dog at this stage of the competition really."