$re = '~(.*)<p[^>]*>.*</p>\R?~ms';
$str = '<p align="justify">First paragraph</p>
<p>Second paragraph</p>
<p>Third paragraph</p>
<div class="item">
<p>Some paragraph here</p>
<p><strong><u>Specs</u>:</strong><br /><br /><strong>Weight:</strong> 10kg<br /><br /><strong>LxWxH:</strong> 5mx1mx40cm</p
<p align="justify">second last para</p>
<p align="justify">This is the paragraph I am trying to remove with regex.</p>
</div>';
$subst = "$1";
$result = preg_replace($re, $subst, $str, 1);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php