Hartzler, who beat long-time incumbent Ike Skelton in 2010, faced a tough challenge from Hensley, the Cass County prosecutor. New 2012 boundaries expanded the district into central Missouri, including Boone County -- traditionally a strong county for Democrats.
With a little more than 1 percent of district precincts reporting, Hartzler led with 68 percent of the ballots cast, compared to Hensley's 30 percent.
The 4th District race has been considered the most competitive of Missouri's eight House races.
Hartzler, 52, has been a reliable vote for Republican positions in the House. She campaigned on proposals to reduce the federal deficit and cut federal regulations, and she has argued repeatedly for increasing defense spending. Missouri's 4th District includes Whiteman AFB and Ft. Leonard Wood.
Hensley, 53, has campaigned on her experience as a lawyer and prosecutor. She hoped to draw Democratic votes in Columbia, Mo., home to the University of Missouri.
Through Oct. 17, Hartzler had raised $1.35 million for her campaign, federal records showed. Hensley had raised $790,501 through the same period.
It's the fourth time the two have campaigned against each other for the House seat. Despite redistricting, and a closer-than-expected 2010 result, Cleaver's seat has been considered secure.
The incumbent's financial problems were an issue in the race. Cleaver is being sued by Bank of America, which claims the former Kansas City mayor defaulted on a $1.5 million loan to buy a car wash.