- preg_replace: documentation ( source)
<?php
$buffered_output = '{"PAC (1) (1)":"\u003Cdiv class=\u0022reference-autocomplete\u0022\u003E \u003Cspan class=\u0022views-field views-field-title\u0022\u003E \u003Cspan class=\u0022field-content\u0022\u003EPAC\u003C\/span\u003E \u003C\/span\u003E \u003Cspan class=\u0022views-field views-field-nid\u0022\u003E \u003Cspan class=\u0022field-content\u0022\u003E(1)\u003C\/span\u003E \u003C\/span\u003E\u003C\/div\u003E"}';
$buffered_output = preg_replace('#(\(\d\)) \1#', '\1', $buffered_output);
echo $buffered_output;