clojure.string/replace-first

(clojure.string/replace-first s match replacement)

Answers s with only the first occurrence of match replaced: a pattern value (#"...", re-pattern) matches by pattern, a literal string or character matches literally. A string replacement over a pattern interpolates $ groups; anything else applies to the match through str. Works as a function value too.

Deviation: match is a pattern value, a literal string or a character -- a string never compiles to a pattern.