Ohio Treasurer Josh Mandel trails Democratic Sen. Sherrod Brown by six points in the latest Quinnipiac University poll.
The latest Quinnipiac University poll, released Thursday morning, shows Brown leads Mandel 46 percent to 40 percent.
Read Quinnipiac Poll in its entirety
The last time Quinnipiac released a poll on the race on March 29, Brown led Mandel 46 percent to 36 percent.
And a February Quinnipiac poll showed Brown up by 13 points, 48 percent to 35 percent.
Brown leads Mandel narrowly among independent voters, 42 percent to 38 percent.
In the previous Quinnipiac poll, Brown held a heftier lead of 46 percent to 28 percent among independents.
Brown leads among women voters by a healthy margin (50 percent to 34 percent), while Mandel leads among men 46 percent to 41 percent.
The March poll showed Brown winning both groups, with a 48 percent to 31 percent lead among women and a 43 percent to 42 percent lead among men.
Since the previous poll, Mandel has released two introductory television ads focused on his military service.
And the race had been expected to tighten, given huge amounts of outside money flowing in and the tight presidential race in the state -- the Chamber of Commerce is the latest to release a major ad buy against Brown.
Regarding the Presidential race, the Quinnipiac poll shows a close race.
President Obama leads presumptive GOP nominee Mitt Romney just 45 to 44 percent, and the two tie at 45 percent if Ohio Sen. Rob Portman is added as Romney's vice-presidential pick.
The Quinnipiac survey was conducted from May 2 - 7, surveying 1,069 registered voters with a margin of error of plus-or-minus 3 percentage points.