Blunt leads current Missouri Secretary of State Kander, 46-44, with Libertarian candidate Jonathan Dine following at 4 percent.
Kander has closed in since Monmouth last polled Missouri's likely voters in August. In that poll, Blunt led by five points, 48-43, with Dine polling at 3 percent.
The Monmouth University poll was conducted Oct. 9-11 among 406 likely voters in Missouri, with a margin of error of plus or minus 4.9 percent.
TPM's PollTracker Average for the U.S. Senate election in Missouri shows a tossup, with Blunt leading Kander, 44 to 43.3.