The European Champions picked up a vital try bonus point as they moved to the top of Pool 6, level on 10 points with London Irish.
But even though his side ruled the roost in almost every phase in Llanelli, Leinster coach Michael Cheika is taking nothing for granted ahead of this weekend's return leg in Dublin.
"Next weekend is a massive game for us. We will never rub out the London Irish defeat until we have beaten them and losing at home to them at the start of the campaign was a real killer for us," said Cheika.
"We pride ourselves on the way we play at home and we want to redeem ourselves in front of our own supporters when we face the Scarlets.
"We may have taken five points at Parc y Scarlets, but that game is over and done with. Now we know we will be facing a fresh challenge at the weekend.
"The Scarlets will want to prove a point when they come to us and I expect more attacking football from them. They will be right up for it and they will be going for everything.
"We were highly motivated coming into the first game and they are going to be exactly the same at the RDS. We know we have got to fight for everything in this tournament and at least after this win we are still very much in the hunt."
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