"No way, no how, no McCain and no Palin," she said as the audience erupted in cheers.
Clinton campaigned heavily in the state in the weeks leading up to her March 4 Democratic primary win, and she returned to economically troubled northeast Ohio on Sunday to urge her supporters to work just as hard for Obama and Joe Biden, the Democratic nominees for president and vice president.
"This election is going to be a game-changer," Clinton said at Lorain County Community College, about 30 miles east of Cleveland. "We have the opportunity to go beyond the failed policies of the last eight years."
Rep. Betty Sutton of Akron, a Clinton supporter during the April and May primaries, introduced a recently laid-off Ohio auto plant worker, who then introduced Clinton.
Keeping her remarks to just 20 minutes, Clinton spoke about the economy, a topic she was expected to address again at a rally in Akron later Sunday.
Clinton recently campaigned for Obama in Florida, another swing state, and was one of several high-profile Democratic women who vouched for Obama in Ohio over the weekend. They included Kansas Gov. Kathleen Sebelius and Arizona Gov. Janet Napolitano.