Roll Call said election results showed Akin, a veteran congressman, had bested wealthy businessman John Brunner and former state Treasurer Sarah Steelman for the chance to block McCaskill from winning a second term. The Washington publication said Akin had 36 percent of the vote with 74 percent of the precincts reporting with Brunner and Steelman too far back to catch up and five other candidates trailing far behind.
Steelman conceded she had lost but Brunner said he wasn't ready to follow suit, the St. Louis Post-Dispatch reported.
Meanwhile, Democratic Gov. Jay Nixon learned he will face Republican Dave Spence in the general election. Spence easily outran Bill Randles, Fred Sauer and John Weiler
A poll released Monday by the Democratic firm Public Policy Polling had shown Brunner in the lead with 35 percent followed by Akin at 30 and Steelman at 25.
Democrats have said they would prefer McCaskill to face Akin.
In Michigan's GOP Senate primary former Rep. Pete Hoekstra defeated businessman Clark Durant, the Detroit Free Press reported. Hoekstra will face Democrat incumbent Debbie Stabenow, considered a major underdog, in the fall.
Former U.S. Rep. Pete Hoekstra beat Republican challenger Clark Durant on Tuesday night, winning the right to face two-term incumbent U.S. Sen. Debbie Stabenow in the fall's general election.
In his concession statement, Durant urged Michiganders to unite behind Hoekstra.
"In November, we all must unite behind candidates who will focus on the solutions to our record debt and spending crisis," he said.
Republicans only need a net gain of four seats to win control of the Senate this fall. The GOP has spent more than $15 million against McCaskill.