$re = '/(.*?\s.*?)\s.*/';
$str = 'eskitirim eski[Verb]-t[Verb+Caus]+[Pos]+Hr[Aor]+YHm[A1sg] : 20.4453125 eski[Verb]-t[Verb+Caus]+[Pos]+Hr[Aor]+Hm[A1sg] : 21.7978515625';
$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