replace-first

Replaces the first instance of match with replacement in s.
  match/replacement can be:
  char / char
 string / string
 pattern / (string or function of match).
  See also replace.
  The replacement is literal (i.e. none of its characters are treated
 specially) for all cases above except pattern / string.
  For pattern / string, $1, $2, etc. in the replacement string are
 substituted with the string that matched the corresponding
 parenthesized group in the pattern.  If you wish your replacement
 string r to be used literally, use (re-quote-replacement r) as the
 replacement argument.  See also documentation for
 java.util.regex.Matcher's appendReplacement method.
  Example:
 (clojure.string/replace-first "swap first two words"
                               #"(\w+)(\s+)(\w+)" "$3$2$1")
 -> "first swap two words"