The unexpected death of Missouri U.S. Senator William J. Stone in April, 1918 prompted Selden Spencer's return to political office. Xenophon P. Wilfley was appointed a temporary replacement until a special election could be held. In November, 1918 Spencer defeated former Governor Joseph W. Folk with 52-percent of the vote to fill the remaining two years of Stone's term. In 1920 Selden Spencer won reelection, first by defeating tennis star-turned-politician Dwight F. Davis in the Republican primary, then Democrat Breckinridge Long by over 121,000 votes in the November general election.