The poll, conducted by Quinnipiac University's Polling Institute, gives McMahon 48 percent support to Murphy's 47, a lead that's within the 2.4 percent margin of error. That's a slight shrinkage in McMahon's lead from the last Quinnipiac poll, in late August, that put her ahead of Murphy by just 3 points.

But two of the last polls, one from a Democratic firm and one independent, have put Murphy slightly ahead. This new poll shows just how persistently close this race remains, even as President Obama pulls far ahead of Mitt Romney in the state.

Both have seen their reputations take a hit from the back-and-forth of the campaign, with those viewing Murphy negatively rising 10 percent and those viewing McMahon negatively rising 6 percent. And while McMahon's seen slightly more favorably, Murphy is underwater, with 40 percent of those polled viewing him unfavorably.

Murphy may be taking a bigger hit than McMahon because, due to her personal wealth, she's had the money to blanket the airwaves this cycle — and that ability has paid off. Eighty-four percent of voters have seen McMahon's campaign ads, while 64 percent have seen Murphy's.

The poll was conducted among 1,696 likely voters from Sept. 28-Oct. 2, and has a margin of error of plus or minus 2.4 percentage points.