The 50 percent to 44 percent margin for Clinton is three percentage points less than one week ago, when she led 52-43.
Obama picked up most strength in the Greater Toledo area, where he had been trailing by 29 percentage points. Tuesday, Obama is only one point behind in that area.
Clinton held on to her lead among Cleveland, Columbus, and Cincinnati area voters, and among moderates and senior citizens.
Obama picked up votes among registered Democrats and voters under the age of 50. Interestingly, among poll respondents who said they had already voted, Clinton leads by 22 percent.
The exclusive poll conducted for WKYC-TV by SurveyUSA included interviews of 2,000 adults in Ohio between Saturday and Monday. Of them, 1,797 were registered to vote and of those, were determined to be likely voters or to have already voted in the Ohio Democratic primary.
Detailed poll results broken down by geography and many demographic groups can be found by clicking on the link below.