That tight race is being driven by Hawaii's ethnic political divide, according to the poll. Schatz, who is white, has a 55 percent to 25 percent lead with white voters over Hanabusa, who is Japanese-American. Hanabusa has a 50 percent to 16 percent lead over Schatz with Native Hawaiian voters and a 42 percent to 27 percent lead over Schatz with Japanese-American voters.

This is the latest poll to show a tight race.

Schatz was named by Hawaii Gov. Neil Abercrombie (D) to fill the remainder of Sen. Daniel Inouye's (D-Hawaii) term after the longtime senator's death. Inouye had requested on his deathbed that Hanabusa be named to the seat, and earlier this year she decided to challenge Schatz for the job.

The poll of 549 registered voters who said they'd vote in the Democratic primary was conducted from Oct. 19-20 and has a margin of error of plus or minus 4.2 percentage points.