Mo. Rev. Stat. § 115.519: Runoff election between tied candidates only.

Only the names of those persons who have received an equal number of votes for nomination to an office at party primary and a higher number of votes than any other candidate for the same office on the same party ballot shall appear on the special primary election ballot. Only the names of those persons who have received an equal number of votes for nomination or election to an office at any other election, and a higher number of votes than any other candidate for the same office at the same election shall appear on the special election ballot.