Democrat Rick Weiland gets 28 percent in the poll, and independent Gordon Howie draws three percent support.
That's a marked improvement for Pressler from the last Survey USA poll, conducted in early September, which gave him a quarter of the vote. Meanwhile, Rounds has lost 4 percent support, and Weiland and Howie haven't moved.
Pressler ran as a Republican, when he served as a U.S. senator between 1979 and 1997, but he endorsed Barack Obama for president in 2008 and 2012.
The poll aligns with other recent polling, with two surveys out in late September giving Pressler about a quarter of the vote and showing Rounds dropping below 40 percent.
The new poll is also the latest to suggest Pressler would easily take down Rounds, if Weiland dropped out of the race. In such a scenario, Pressler would take 54 percent support, while Rounds would draw 39 percent support.
Weiland is also more competitive against Rounds in a head-to-head match-up, but he ties the race if Pressler drops out, as both he and Rounds draw 47 percent support.
The survey shows Rounds is bleeding support from his base, with 55 percent of Republicans backing him in a four-way match-up. And 56 percent say he needs to say more to address the controversy surrounding the state's EB-5 visa program, which traded visas to foreign investors willing to commit at least half a million in funds to local projects.
Democrats have accused Rounds of mismanagement of the program during his time as governor, and it is featured prominently in attack ads from both Weiland and outside groups backing him.
Still, Republicans are heavily favored to pick up the seat this fall due to the red lean of the state.
The survey was conducted among 616 likely voters from Oct. 1-5 and has a margin of error of 4 percent.