(CNN) - New polls released Thursday indicate three competitive Senate races remain tight in Ohio, Wisconsin and Florida, according to surveys by Quinnipiac University, CBS News, and The New York Times.
Starting with Florida, where Democratic incumbent Sen. Bill Nelson is defending his seat against Republican challenger Rep. Connie Mack, the two-term senator leads Mack, 50% to 41%, respectively.
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The new results marked an uptick for both candidates from a similar poll released Aug. 1, though Nelson saw more of an increase. At the time, 47% of voters said they would back Nelson and 40% said they would pick Mack.
While Mack, a four-term congressman, has long been the Republican favorite, he did not seal up the nomination until last week's primary in the Sunshine State.
In the new poll released Thursday, independent voters were divided, with 45% supporting Nelson and 43% favoring Mack.
Meanwhile in Ohio, Democratic incumbent Sen. Sherrod Brown faces a heated contest against state treasurer Josh Mandel. According to the new poll, the first-term senator leads his Republican challenger, 48% to 41%. The margin for independent voters was tighter, with 43% saying they would back Mandel and 43% saying the same thing about Brown.
In another poll released Thursday, however, the race appears to be closer between the two candidates. According to the Ohio Poll by the University of Cincinnati, Brown only has a one-point advantage over Mandel, 48% to 47%, a margin that falls well within the sampling error.
Over in Wisconsin, where former Gov. Tommy Thompson locked up the nomination last week in a crowded Republican primary, the former governor leads his Democratic opponent, Rep. Tammy Baldwin, according to the Quinnipiac University/CBS News/New York Times survey.
The two candidates are competing in an open contest to replace Sen. Herb Kohl, a four-term Democrat who is not running for re-election. With less than three months before the November election, Thompson leads Baldwin by a slim margin of 50% to 44%. Independent voters, meanwhile, more heavily favor Thompson, 54%-39%.
All three states represent critical battlegrounds in the presidential election. The same surveys also showed Mitt Romney and President Barack Obama tied in Wisconsin, Florida and Ohio.
Quinnipiac University, in cooperation with CBS News and The New York Times, surveyed 1,241 likely voters in Florida, 1,253 likely voters in Ohio, and 1,190 likely voters in Wisconsin. The survey was conducted by telephone between August 15 and August 21, and all three surveys had a sampling error of plus or minus 2.8 percentage points.
For the other Ohio poll, the Institute for Policy Research at the University of Cincinnati questioned by telephone 802 likely voters by telephone between August 16 and August 21. The sampling error is plus or minus 3.4 percent percentage points.
- CNN Political Editor Paul Steinhauser contributed to this report.