Lt. Gov. Mike Kehoe of Missouri won the Republican primary for governor on Tuesday, according to The Associated Press, giving him the upper hand in a contest in November to succeed Mike Parson.

Mr. Kehoe, 62, defeated two rivals who portrayed themselves as more conservative alternatives to the current state leadership. They included Missouri’s secretary of state, Jay Ashcroft, the son of the former Missouri governor and U.S. senator and attorney general John Ashcroft. Jay Ashcroft finished third behind State Senator Bill Eigel, who pledged to act aggressively to expel all undocumented immigrants from Missouri.

Mr. Parson, 68, who has served as governor since June 2018 and remains broadly popular, is barred by term limits from running this year. He endorsed Mr. Kehoe last month.

In the Democratic primary, State Representative Crystal Quade, the House minority leader, defeated Mike Hamra, a businessman.

Democrats had long been competitive in national and statewide races in Missouri. The state had a Democratic governor, Jay Nixon, as recently as 2017 and a Democrat in the U.S. Senate, Claire McCaskill, as recently as 2019. Former President Barack Obama narrowly lost Missouri in 2008.

But the election of former President Donald J. Trump in 2016 made clear that Missouri had turned into a solidly red state. That means that the winner of the Republican primary is widely expected to become the next governor, said Daniel Butler, a political scientist at Washington University in St. Louis.