Trump has 45 percent support, while Clinton trails with 42, putting just within the poll's margin of error.
Clinton rival Bernie Sanders, meanwhile, leads Trump 46 to 42, according to the same poll.
The presumptive GOP nominee is buoyed by his support among whites, leading Clinton 55 to 31 percent. That margin grows among whites without a college degree, 61 percent of whom favor Trump, while just 24 percent back Clinton.
But the real estate mogul still struggles with women voters, half of whom back Clinton, and just 36 percent support Trump.
The former secretary of State also holds commanding leads Trump among blacks (90 to 7 percent) and Hispanics (62 to 23 percent).
The poll surveyed 1,021 registered voters from May 14-17. It has a margin of error of 3 points.