Barnes later fired back with her own bristling ad that claimed Graves failed to pay taxes on airplanes he owned and benefited from a sweetheart deal to renovate the Tarkio airport on land his family had a right to reclaim. Local officials had denied both claims.
The 9th District race saw Luetkemeyer, a former state lawmaker and Missouri tourism director from St. Elizabeth, pour about $1.5 million of his own money into the contest to keep up with Baker's fundraising.
National Democrats, sensing the chance to pick up a Republican seat, have spent about $1 million on television ads to boost Baker, a state House member from Columbia.
Meanwhile, in the state's seven other House districts, incumbent lawmakers easily defeated lesser known rivals.
The Associated Press declared the winners based on an analysis of current returns, voter turnout and previous voting patterns.
• Democratic Rep. William Lacy Clay defeated Libertarian Robb Cunningham in the 1st District of St. Louis.
• Republican Rep. Todd Akin beat Democrat Bill Haas in the St. Louis County-area 2nd District.
• Democratic Rep. Russ Carnahan defeated Republican Chris Sander in St. Louis' 3rd District.
• Democratic Rep. Ike Skelton beat Republican Jeff Parnell in central and western Missouri's 4th District.
• Democratic Rep. Emanuel Cleaver defeated Republican Jacob Turk in Kansas City's 5th District.
• Republican Rep. Roy Blunt beat Democrat Richard Monroe in southwest Missouri's 7th District.
• Republican Rep. Jo Ann Emerson defeated Democrat Joe Allen in southeast Missouri's 8th District.
• The state will no longer require gamblers to limit their losses at casinos, ending a rule that did not exist in any other state in the country.
Removal of the loss limits and changes in other casino regulations was forecast to bring in millions more in revenue for the state's schools and local services — all without raising taxes.
Proposition A, called the "Schools First Elementary and Secondary Education Funding Initiative," was one of five statewide issues approved by voters Tuesday.
It repeals the $500 loss limit at casinos, caps the licensing of new casinos and raises taxes on existing ones. Supporters said it also would allow Missouri casinos to compete more effectively with casinos in neighboring states that do not have loss limits.
With 98% of the precincts reporting, Proposition A won approval of 56% of voters.
The gambling initiative — funded almost entirely by the owners of Missouri's casinos — was forecast to raise more than $100 million a year in additional revenue for schools and local services.
"The approval of Proposition A, the Schools First Initiative, by Missouri voters is a win for our state's economy, our schools and common sense," said Scott Charton, spokesman for the YES on A Coalition, which spearheaded the effort.
"It means Missouri can finally compete for casino visitors and revenues on a level playing field with neighboring states, and it means there will be more revenues to help fund elementary and secondary education from the gaming tax paid by casinos."
Currently, Missouri requires gamblers who lose up to $500 in two hours to wait until the next two-hour "excursion" before buying up to $500 more in chips or tokens.