Wales slipped to a 26-12 defeat at the Millennium Stadium as two tries in the space of five minutes by wingers Juan Jose Imhoff and Gonzalo Camacho secured victory for the Pumas.
Leigh Halfpenny kicked three penalties as Wales led 9-6 at the break but the two Argentinian tries consigned them to defeat.
McCusker admits Saturday’s result was disappointing but believes Wales have the perfect opportunity to bounce back against Samoa.
“Argentina are getting better year on year and unfortunately we were the latest victims,” he said.
“They’ve got a talisman in Lobbe and we didn’t really do enough to keep him quiet. There were periods where we thought we had them on the rack but just let them off the hook which is unfortunate.
“And after those two tries we just couldn’t get the ball back.”
With a short turnaround ahead of Friday’s clash with Samoa, Wales won’t have to wait long before returning to competitive action.
They take on a Samoa side who dispatched Canada 42-13 at Colwyn Bay, winger Robert Lilomaiava helping himself to four tries on debut.
“We’re eager to get back on the pitch and put some wrongs right so we’re looking forward to Friday night,” added McCusker.
“I think Samoa will be very physical but whether they’ve got the experience of playing high level test rugby we’ll see on Friday.”
