The poll, conducted by Harstad Strategic Research for the Democratic Senatorial Campaign Committee, gives Warren 50 percent support to Brown's 46.

It's a flip in fortunes for the Democrat since the last DSCC poll, taken in August, which gave Brown 47 percent support to Warren's 44. And this new poll shows a lead similar to an independent survey released Sunday, which gave her a 5-point lead over Brown.

The polling memo also reveals that more of those surveyed say there is "a fair chance" that they would support Warren over Brown, with 6 percent saying so of the Democrat and only 4 percent saying so of the Republican, indicating Warren has a higher number of potential voters at this point than Brown.

Warren has had the momentum for much of the past month, posting a lead in nearly every poll out since mid-September. But Brown and his campaign have launched newly negative ads, and the freshman senator has come out on the attack against Warren in both of their debates, questioning her character and charging her with hypocrisy over her corporate legal clients.

But the new memo from the DSCC suggests this strategy might be working against Brown, as 48 percent say they are less likely to vote for him "based on what they have heard lately." Forty-two percent of those surveyed say the same of Warren.

The poll was conducted among 602 likely voters from Oct. 2-4 and has a margin of error of plus or minus 4 percentage points.