Mo. Rev. Stat. § 78.510
The primary election as provided for by sections 78.470 to 78.500 shall not be required if upon the expiration of the time for filing of statements with the city clerk of persons desiring to become a candidate for councilman, as provided for by sections 78.470 to 78.500, the number of such persons shall not exceed a number equal to twice the number to be elected at the general or special election. Within forty-eight hours after the expiration of the time for filing of such statements with the city clerk the council shall canvass the statements filed to determine from the number of statements filed whether this section shall be applicable. In the event that it is determined that the provisions shall be applicable the council shall, by ordinance, provide that a primary election under the provisions of sections 78.470 to 78.500 shall not be held and that the names of the persons filing statements shall be printed on the municipal election ballots as the nominees for councilman as provided for by sections 78.520 to 78.540; provided, however, that the names of such persons appearing on such ballot shall appear thereon in the order that they were filed with the city clerk.
§ 78.510, RSMo