Despite leading 16-10 at half-time the west Wales region kicked-off the RaboDirect Pro12 season with a heavy 42-19 defeat after a second-half implosion.
They return to action against Benetton Treviso on Saturday and McCusker, who scored the Scarlets’ only try, admits they cannot afford to surrender another lead.
“Turnovers killed us and we weren’t able to flip from attack to defence very well, it seemed as if we were chasing shadows in the end,” said the Wales international.
“Leinster probably took a lot of confidence from being only 16-10 down at half-time knowing they hadn’t done that much in the game.
“We didn’t turn our control into points.
“In the second half it seemed like we were running backwards and passing forwards for long periods, we killed ourselves.
“It has to be about consistency, we can’t just play for 20 or 30 minutes. It happened last year in Clermont, we are just not consistent enough at the moment.”
But McCusker has refused to push the panic button after just one game of the Pro12 season and reckons the Scarlets can easily put things right.
“It is only one game. We will be lost if we didn’t show anything and just got hammered,” added McCusker.
“We showed what we can do in that first half.”
