The poll from Suffolk University and WHDH-TV, Boston, shows a shift from previous polls that had given Warren the upper hand, The Hill reported Friday.
A December University of Massachusetts and Boston Herald poll had Warren up by 7 points and a WBUR-Radio, Boston, poll this month gave Warren a 3-point edge.
Brown recently created controversy, The Hill said, by choosing to back a Senate amendment that would allow insurers and employers to deny medical coverage for things they find objectionable, such as birth control.
"I am shocked that Sen. Brown jumped in to support such an extreme measure," Warren told The Washington Post Tuesday. "This is an all new attack on healthcare. Any insurance company could leave anyone without healthcare, just when they need it most."