Democratic incumbent Sherrod Brown said all Republican challenger Josh Mandel does is "attack, attack, attack."
Mandel said all Brown gives you is "Washington speak."
One feisty exchange was over efforts to regulate the use of coal and force the closing of coal powered utility plants.
"Ladies and gentlemen, there is a war on coal in this country," declared Mandel. "And while President Obama is the general, Sherrod Brown is his main lieutenant."
Brown denied that such a war existed, and said the coal industry has actually thrived during his Senate term.
"There are more coal jobs and more coal produced in Ohio than there were five years ago, despite the talking points and the yard signs."
Both candidates accused the other of neglecting the middle class. Two more debates are scheduled later this month.