Daniel Hourcade rued a poor defensive display as Argentina were beaten 36-20 by Australia in the Rugby Championship on Saturday.
Defeat for the Pumas handed New Zealand the title for a fourth time, their first-half performance in Perth particularly worrying for Hourcade as they conceded 21 points.
Tries from Samu Kerevi, Sane Hylett-Petty and Will Genia put Australia firmly in the box seat, leaving the Pumas struggling for consistency.
In response they could only manage six points, and although they improved after the break they continued to struggle to keep the Wallabies at bay.
Michael Hooper and Genia wrapped up victory for the hosts, and Hourcade was left frustrated by his side's fragmented display.
"We started badly and were then disoriented on the field and did not react. We conceded 21 points to simple moves," said the coach.
"We started well in the second, but then they also reacted. We had a bad defence and that was the key. Errors in attack I can understand, but defensive mistakes and not paying attention, no.
"They are basic errors that we cannot commit, we know that if you mess up at this level, you concede points."