McCaskill declared victory and returns early Wednesday showed her leading 50 percent to 47 percent with 98 percent of the precincts reporting.
"Tonight we have heard the voice of Missourians and they have said we want change," McCaskill said.
The St. Louis Post-Dispatch said McCaskill was able to capture voters in the state's solidly Republican rural counties, winning more than 40 percent in Southwest Missouri's Greene County. Exit polls showed Missouri voters were deeply concerned about the economy and the war in Iraq.
"The headwind was very strong this year," Talent said in concession remarks about 1 a.m.